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@@ -618,3 +618,4 @@ valley/lib/python3.10/site-packages/gradio/templates/frontend/static/img/Duck.gl
 valley/lib/python3.10/site-packages/tokenizers.libs/libgssapi_krb5-bb73e344.so.2.2 filter=lfs diff=lfs merge=lfs -text
 valley/lib/python3.10/site-packages/tokenizers.libs/libssl-09014658.so.1.0.1e filter=lfs diff=lfs merge=lfs -text
 valley/lib/python3.10/site-packages/gradio/templates/cdn/static/img/Duck.glb filter=lfs diff=lfs merge=lfs -text
+valley/lib/python3.10/site-packages/pandas/core/__pycache__/generic.cpython-310.pyc filter=lfs diff=lfs merge=lfs -text

valley/lib/python3.10/site-packages/pandas/core/__pycache__/generic.cpython-310.pyc

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:65629dba97e25844d35d97f17d655130a12e68e0249ea879ca6d476ef458dcc4
+size 385653

valley/lib/python3.10/site-packages/pandas/tests/config/test_config.py

@@ -0,0 +1,437 @@
+import pytest
+
+from pandas._config import config as cf
+from pandas._config.config import OptionError
+
+import pandas as pd
+import pandas._testing as tm
+
+
+class TestConfig:
+    @pytest.fixture(autouse=True)
+    def clean_config(self, monkeypatch):
+        with monkeypatch.context() as m:
+            m.setattr(cf, "_global_config", {})
+            m.setattr(cf, "options", cf.DictWrapper(cf._global_config))
+            m.setattr(cf, "_deprecated_options", {})
+            m.setattr(cf, "_registered_options", {})
+
+            # Our test fixture in conftest.py sets "chained_assignment"
+            # to "raise" only after all test methods have been setup.
+            # However, after this setup, there is no longer any
+            # "chained_assignment" option, so re-register it.
+            cf.register_option("chained_assignment", "raise")
+            yield
+
+    def test_api(self):
+        # the pandas object exposes the user API
+        assert hasattr(pd, "get_option")
+        assert hasattr(pd, "set_option")
+        assert hasattr(pd, "reset_option")
+        assert hasattr(pd, "describe_option")
+
+    def test_is_one_of_factory(self):
+        v = cf.is_one_of_factory([None, 12])
+
+        v(12)
+        v(None)
+        msg = r"Value must be one of None\|12"
+        with pytest.raises(ValueError, match=msg):
+            v(1.1)
+
+    def test_register_option(self):
+        cf.register_option("a", 1, "doc")
+
+        # can't register an already registered option
+        msg = "Option 'a' has already been registered"
+        with pytest.raises(OptionError, match=msg):
+            cf.register_option("a", 1, "doc")
+
+        # can't register an already registered option
+        msg = "Path prefix to option 'a' is already an option"
+        with pytest.raises(OptionError, match=msg):
+            cf.register_option("a.b.c.d1", 1, "doc")
+        with pytest.raises(OptionError, match=msg):
+            cf.register_option("a.b.c.d2", 1, "doc")
+
+        # no python keywords
+        msg = "for is a python keyword"
+        with pytest.raises(ValueError, match=msg):
+            cf.register_option("for", 0)
+        with pytest.raises(ValueError, match=msg):
+            cf.register_option("a.for.b", 0)
+        # must be valid identifier (ensure attribute access works)
+        msg = "oh my goddess! is not a valid identifier"
+        with pytest.raises(ValueError, match=msg):
+            cf.register_option("Oh my Goddess!", 0)
+
+        # we can register options several levels deep
+        # without predefining the intermediate steps
+        # and we can define differently named options
+        # in the same namespace
+        cf.register_option("k.b.c.d1", 1, "doc")
+        cf.register_option("k.b.c.d2", 1, "doc")
+
+    def test_describe_option(self):
+        cf.register_option("a", 1, "doc")
+        cf.register_option("b", 1, "doc2")
+        cf.deprecate_option("b")
+
+        cf.register_option("c.d.e1", 1, "doc3")
+        cf.register_option("c.d.e2", 1, "doc4")
+        cf.register_option("f", 1)
+        cf.register_option("g.h", 1)
+        cf.register_option("k", 2)
+        cf.deprecate_option("g.h", rkey="k")
+        cf.register_option("l", "foo")
+
+        # non-existent keys raise KeyError
+        msg = r"No such keys\(s\)"
+        with pytest.raises(OptionError, match=msg):
+            cf.describe_option("no.such.key")
+
+        # we can get the description for any key we registered
+        assert "doc" in cf.describe_option("a", _print_desc=False)
+        assert "doc2" in cf.describe_option("b", _print_desc=False)
+        assert "precated" in cf.describe_option("b", _print_desc=False)
+        assert "doc3" in cf.describe_option("c.d.e1", _print_desc=False)
+        assert "doc4" in cf.describe_option("c.d.e2", _print_desc=False)
+
+        # if no doc is specified we get a default message
+        # saying "description not available"
+        assert "available" in cf.describe_option("f", _print_desc=False)
+        assert "available" in cf.describe_option("g.h", _print_desc=False)
+        assert "precated" in cf.describe_option("g.h", _print_desc=False)
+        assert "k" in cf.describe_option("g.h", _print_desc=False)
+
+        # default is reported
+        assert "foo" in cf.describe_option("l", _print_desc=False)
+        # current value is reported
+        assert "bar" not in cf.describe_option("l", _print_desc=False)
+        cf.set_option("l", "bar")
+        assert "bar" in cf.describe_option("l", _print_desc=False)
+
+    def test_case_insensitive(self):
+        cf.register_option("KanBAN", 1, "doc")
+
+        assert "doc" in cf.describe_option("kanbaN", _print_desc=False)
+        assert cf.get_option("kanBaN") == 1
+        cf.set_option("KanBan", 2)
+        assert cf.get_option("kAnBaN") == 2
+
+        # gets of non-existent keys fail
+        msg = r"No such keys\(s\): 'no_such_option'"
+        with pytest.raises(OptionError, match=msg):
+            cf.get_option("no_such_option")
+        cf.deprecate_option("KanBan")
+
+        assert cf._is_deprecated("kAnBaN")
+
+    def test_get_option(self):
+        cf.register_option("a", 1, "doc")
+        cf.register_option("b.c", "hullo", "doc2")
+        cf.register_option("b.b", None, "doc2")
+
+        # gets of existing keys succeed
+        assert cf.get_option("a") == 1
+        assert cf.get_option("b.c") == "hullo"
+        assert cf.get_option("b.b") is None
+
+        # gets of non-existent keys fail
+        msg = r"No such keys\(s\): 'no_such_option'"
+        with pytest.raises(OptionError, match=msg):
+            cf.get_option("no_such_option")
+
+    def test_set_option(self):
+        cf.register_option("a", 1, "doc")
+        cf.register_option("b.c", "hullo", "doc2")
+        cf.register_option("b.b", None, "doc2")
+
+        assert cf.get_option("a") == 1
+        assert cf.get_option("b.c") == "hullo"
+        assert cf.get_option("b.b") is None
+
+        cf.set_option("a", 2)
+        cf.set_option("b.c", "wurld")
+        cf.set_option("b.b", 1.1)
+
+        assert cf.get_option("a") == 2
+        assert cf.get_option("b.c") == "wurld"
+        assert cf.get_option("b.b") == 1.1
+
+        msg = r"No such keys\(s\): 'no.such.key'"
+        with pytest.raises(OptionError, match=msg):
+            cf.set_option("no.such.key", None)
+
+    def test_set_option_empty_args(self):
+        msg = "Must provide an even number of non-keyword arguments"
+        with pytest.raises(ValueError, match=msg):
+            cf.set_option()
+
+    def test_set_option_uneven_args(self):
+        msg = "Must provide an even number of non-keyword arguments"
+        with pytest.raises(ValueError, match=msg):
+            cf.set_option("a.b", 2, "b.c")
+
+    def test_set_option_invalid_single_argument_type(self):
+        msg = "Must provide an even number of non-keyword arguments"
+        with pytest.raises(ValueError, match=msg):
+            cf.set_option(2)
+
+    def test_set_option_multiple(self):
+        cf.register_option("a", 1, "doc")
+        cf.register_option("b.c", "hullo", "doc2")
+        cf.register_option("b.b", None, "doc2")
+
+        assert cf.get_option("a") == 1
+        assert cf.get_option("b.c") == "hullo"
+        assert cf.get_option("b.b") is None
+
+        cf.set_option("a", "2", "b.c", None, "b.b", 10.0)
+
+        assert cf.get_option("a") == "2"
+        assert cf.get_option("b.c") is None
+        assert cf.get_option("b.b") == 10.0
+
+    def test_validation(self):
+        cf.register_option("a", 1, "doc", validator=cf.is_int)
+        cf.register_option("d", 1, "doc", validator=cf.is_nonnegative_int)
+        cf.register_option("b.c", "hullo", "doc2", validator=cf.is_text)
+
+        msg = "Value must have type '<class 'int'>'"
+        with pytest.raises(ValueError, match=msg):
+            cf.register_option("a.b.c.d2", "NO", "doc", validator=cf.is_int)
+
+        cf.set_option("a", 2)  # int is_int
+        cf.set_option("b.c", "wurld")  # str is_str
+        cf.set_option("d", 2)
+        cf.set_option("d", None)  # non-negative int can be None
+
+        # None not is_int
+        with pytest.raises(ValueError, match=msg):
+            cf.set_option("a", None)
+        with pytest.raises(ValueError, match=msg):
+            cf.set_option("a", "ab")
+
+        msg = "Value must be a nonnegative integer or None"
+        with pytest.raises(ValueError, match=msg):
+            cf.register_option("a.b.c.d3", "NO", "doc", validator=cf.is_nonnegative_int)
+        with pytest.raises(ValueError, match=msg):
+            cf.register_option("a.b.c.d3", -2, "doc", validator=cf.is_nonnegative_int)
+
+        msg = r"Value must be an instance of <class 'str'>\|<class 'bytes'>"
+        with pytest.raises(ValueError, match=msg):
+            cf.set_option("b.c", 1)
+
+        validator = cf.is_one_of_factory([None, cf.is_callable])
+        cf.register_option("b", lambda: None, "doc", validator=validator)
+        # pylint: disable-next=consider-using-f-string
+        cf.set_option("b", "%.1f".format)  # Formatter is callable
+        cf.set_option("b", None)  # Formatter is none (default)
+        with pytest.raises(ValueError, match="Value must be a callable"):
+            cf.set_option("b", "%.1f")
+
+    def test_reset_option(self):
+        cf.register_option("a", 1, "doc", validator=cf.is_int)
+        cf.register_option("b.c", "hullo", "doc2", validator=cf.is_str)
+        assert cf.get_option("a") == 1
+        assert cf.get_option("b.c") == "hullo"
+
+        cf.set_option("a", 2)
+        cf.set_option("b.c", "wurld")
+        assert cf.get_option("a") == 2
+        assert cf.get_option("b.c") == "wurld"
+
+        cf.reset_option("a")
+        assert cf.get_option("a") == 1
+        assert cf.get_option("b.c") == "wurld"
+        cf.reset_option("b.c")
+        assert cf.get_option("a") == 1
+        assert cf.get_option("b.c") == "hullo"
+
+    def test_reset_option_all(self):
+        cf.register_option("a", 1, "doc", validator=cf.is_int)
+        cf.register_option("b.c", "hullo", "doc2", validator=cf.is_str)
+        assert cf.get_option("a") == 1
+        assert cf.get_option("b.c") == "hullo"
+
+        cf.set_option("a", 2)
+        cf.set_option("b.c", "wurld")
+        assert cf.get_option("a") == 2
+        assert cf.get_option("b.c") == "wurld"
+
+        cf.reset_option("all")
+        assert cf.get_option("a") == 1
+        assert cf.get_option("b.c") == "hullo"
+
+    def test_deprecate_option(self):
+        # we can deprecate non-existent options
+        cf.deprecate_option("foo")
+
+        assert cf._is_deprecated("foo")
+        with tm.assert_produces_warning(FutureWarning, match="deprecated"):
+            with pytest.raises(KeyError, match="No such keys.s.: 'foo'"):
+                cf.get_option("foo")
+
+        cf.register_option("a", 1, "doc", validator=cf.is_int)
+        cf.register_option("b.c", "hullo", "doc2")
+        cf.register_option("foo", "hullo", "doc2")
+
+        cf.deprecate_option("a", removal_ver="nifty_ver")
+        with tm.assert_produces_warning(FutureWarning, match="eprecated.*nifty_ver"):
+            cf.get_option("a")
+
+            msg = "Option 'a' has already been defined as deprecated"
+            with pytest.raises(OptionError, match=msg):
+                cf.deprecate_option("a")
+
+        cf.deprecate_option("b.c", "zounds!")
+        with tm.assert_produces_warning(FutureWarning, match="zounds!"):
+            cf.get_option("b.c")
+
+        # test rerouting keys
+        cf.register_option("d.a", "foo", "doc2")
+        cf.register_option("d.dep", "bar", "doc2")
+        assert cf.get_option("d.a") == "foo"
+        assert cf.get_option("d.dep") == "bar"
+
+        cf.deprecate_option("d.dep", rkey="d.a")  # reroute d.dep to d.a
+        with tm.assert_produces_warning(FutureWarning, match="eprecated"):
+            assert cf.get_option("d.dep") == "foo"
+
+        with tm.assert_produces_warning(FutureWarning, match="eprecated"):
+            cf.set_option("d.dep", "baz")  # should overwrite "d.a"
+
+        with tm.assert_produces_warning(FutureWarning, match="eprecated"):
+            assert cf.get_option("d.dep") == "baz"
+
+    def test_config_prefix(self):
+        with cf.config_prefix("base"):
+            cf.register_option("a", 1, "doc1")
+            cf.register_option("b", 2, "doc2")
+            assert cf.get_option("a") == 1
+            assert cf.get_option("b") == 2
+
+            cf.set_option("a", 3)
+            cf.set_option("b", 4)
+            assert cf.get_option("a") == 3
+            assert cf.get_option("b") == 4
+
+        assert cf.get_option("base.a") == 3
+        assert cf.get_option("base.b") == 4
+        assert "doc1" in cf.describe_option("base.a", _print_desc=False)
+        assert "doc2" in cf.describe_option("base.b", _print_desc=False)
+
+        cf.reset_option("base.a")
+        cf.reset_option("base.b")
+
+        with cf.config_prefix("base"):
+            assert cf.get_option("a") == 1
+            assert cf.get_option("b") == 2
+
+    def test_callback(self):
+        k = [None]
+        v = [None]
+
+        def callback(key):
+            k.append(key)
+            v.append(cf.get_option(key))
+
+        cf.register_option("d.a", "foo", cb=callback)
+        cf.register_option("d.b", "foo", cb=callback)
+
+        del k[-1], v[-1]
+        cf.set_option("d.a", "fooz")
+        assert k[-1] == "d.a"
+        assert v[-1] == "fooz"
+
+        del k[-1], v[-1]
+        cf.set_option("d.b", "boo")
+        assert k[-1] == "d.b"
+        assert v[-1] == "boo"
+
+        del k[-1], v[-1]
+        cf.reset_option("d.b")
+        assert k[-1] == "d.b"
+
+    def test_set_ContextManager(self):
+        def eq(val):
+            assert cf.get_option("a") == val
+
+        cf.register_option("a", 0)
+        eq(0)
+        with cf.option_context("a", 15):
+            eq(15)
+            with cf.option_context("a", 25):
+                eq(25)
+            eq(15)
+        eq(0)
+
+        cf.set_option("a", 17)
+        eq(17)
+
+        # Test that option_context can be used as a decorator too (#34253).
+        @cf.option_context("a", 123)
+        def f():
+            eq(123)
+
+        f()
+
+    def test_attribute_access(self):
+        holder = []
+
+        def f3(key):
+            holder.append(True)
+
+        cf.register_option("a", 0)
+        cf.register_option("c", 0, cb=f3)
+        options = cf.options
+
+        assert options.a == 0
+        with cf.option_context("a", 15):
+            assert options.a == 15
+
+        options.a = 500
+        assert cf.get_option("a") == 500
+
+        cf.reset_option("a")
+        assert options.a == cf.get_option("a", 0)
+
+        msg = "You can only set the value of existing options"
+        with pytest.raises(OptionError, match=msg):
+            options.b = 1
+        with pytest.raises(OptionError, match=msg):
+            options.display = 1
+
+        # make sure callback kicks when using this form of setting
+        options.c = 1
+        assert len(holder) == 1
+
+    def test_option_context_scope(self):
+        # Ensure that creating a context does not affect the existing
+        # environment as it is supposed to be used with the `with` statement.
+        # See https://github.com/pandas-dev/pandas/issues/8514
+
+        original_value = 60
+        context_value = 10
+        option_name = "a"
+
+        cf.register_option(option_name, original_value)
+
+        # Ensure creating contexts didn't affect the current context.
+        ctx = cf.option_context(option_name, context_value)
+        assert cf.get_option(option_name) == original_value
+
+        # Ensure the correct value is available inside the context.
+        with ctx:
+            assert cf.get_option(option_name) == context_value
+
+        # Ensure the current context is reset
+        assert cf.get_option(option_name) == original_value
+
+    def test_dictwrapper_getattr(self):
+        options = cf.options
+        # GH 19789
+        with pytest.raises(OptionError, match="No such option"):
+            options.bananas
+        assert not hasattr(options, "bananas")

valley/lib/python3.10/site-packages/pandas/tests/config/test_localization.py

@@ -0,0 +1,156 @@
+import codecs
+import locale
+import os
+
+import pytest
+
+from pandas._config.localization import (
+    can_set_locale,
+    get_locales,
+    set_locale,
+)
+
+from pandas.compat import ISMUSL
+
+import pandas as pd
+
+_all_locales = get_locales()
+_current_locale = locale.setlocale(locale.LC_ALL)  # getlocale() is wrong, see GH#46595
+
+# Don't run any of these tests if we have no locales.
+pytestmark = pytest.mark.skipif(not _all_locales, reason="Need locales")
+
+_skip_if_only_one_locale = pytest.mark.skipif(
+    len(_all_locales) <= 1, reason="Need multiple locales for meaningful test"
+)
+
+
+def _get_current_locale(lc_var: int = locale.LC_ALL) -> str:
+    # getlocale is not always compliant with setlocale, use setlocale. GH#46595
+    return locale.setlocale(lc_var)
+
+
+@pytest.mark.parametrize("lc_var", (locale.LC_ALL, locale.LC_CTYPE, locale.LC_TIME))
+def test_can_set_current_locale(lc_var):
+    # Can set the current locale
+    before_locale = _get_current_locale(lc_var)
+    assert can_set_locale(before_locale, lc_var=lc_var)
+    after_locale = _get_current_locale(lc_var)
+    assert before_locale == after_locale
+
+
+@pytest.mark.parametrize("lc_var", (locale.LC_ALL, locale.LC_CTYPE, locale.LC_TIME))
+def test_can_set_locale_valid_set(lc_var):
+    # Can set the default locale.
+    before_locale = _get_current_locale(lc_var)
+    assert can_set_locale("", lc_var=lc_var)
+    after_locale = _get_current_locale(lc_var)
+    assert before_locale == after_locale
+
+
+@pytest.mark.parametrize(
+    "lc_var",
+    (
+        locale.LC_ALL,
+        locale.LC_CTYPE,
+        pytest.param(
+            locale.LC_TIME,
+            marks=pytest.mark.skipif(
+                ISMUSL, reason="MUSL allows setting invalid LC_TIME."
+            ),
+        ),
+    ),
+)
+def test_can_set_locale_invalid_set(lc_var):
+    # Cannot set an invalid locale.
+    before_locale = _get_current_locale(lc_var)
+    assert not can_set_locale("non-existent_locale", lc_var=lc_var)
+    after_locale = _get_current_locale(lc_var)
+    assert before_locale == after_locale
+
+
+@pytest.mark.parametrize(
+    "lang,enc",
+    [
+        ("it_CH", "UTF-8"),
+        ("en_US", "ascii"),
+        ("zh_CN", "GB2312"),
+        ("it_IT", "ISO-8859-1"),
+    ],
+)
+@pytest.mark.parametrize("lc_var", (locale.LC_ALL, locale.LC_CTYPE, locale.LC_TIME))
+def test_can_set_locale_no_leak(lang, enc, lc_var):
+    # Test that can_set_locale does not leak even when returning False. See GH#46595
+    before_locale = _get_current_locale(lc_var)
+    can_set_locale((lang, enc), locale.LC_ALL)
+    after_locale = _get_current_locale(lc_var)
+    assert before_locale == after_locale
+
+
+def test_can_set_locale_invalid_get(monkeypatch):
+    # see GH#22129
+    # In some cases, an invalid locale can be set,
+    #  but a subsequent getlocale() raises a ValueError.
+
+    def mock_get_locale():
+        raise ValueError()
+
+    with monkeypatch.context() as m:
+        m.setattr(locale, "getlocale", mock_get_locale)
+        assert not can_set_locale("")
+
+
+def test_get_locales_at_least_one():
+    # see GH#9744
+    assert len(_all_locales) > 0
+
+
+@_skip_if_only_one_locale
+def test_get_locales_prefix():
+    first_locale = _all_locales[0]
+    assert len(get_locales(prefix=first_locale[:2])) > 0
+
+
+@_skip_if_only_one_locale
+@pytest.mark.parametrize(
+    "lang,enc",
+    [
+        ("it_CH", "UTF-8"),
+        ("en_US", "ascii"),
+        ("zh_CN", "GB2312"),
+        ("it_IT", "ISO-8859-1"),
+    ],
+)
+def test_set_locale(lang, enc):
+    before_locale = _get_current_locale()
+
+    enc = codecs.lookup(enc).name
+    new_locale = lang, enc
+
+    if not can_set_locale(new_locale):
+        msg = "unsupported locale setting"
+
+        with pytest.raises(locale.Error, match=msg):
+            with set_locale(new_locale):
+                pass
+    else:
+        with set_locale(new_locale) as normalized_locale:
+            new_lang, new_enc = normalized_locale.split(".")
+            new_enc = codecs.lookup(enc).name
+
+            normalized_locale = new_lang, new_enc
+            assert normalized_locale == new_locale
+
+    # Once we exit the "with" statement, locale should be back to what it was.
+    after_locale = _get_current_locale()
+    assert before_locale == after_locale
+
+
+def test_encoding_detected():
+    system_locale = os.environ.get("LC_ALL")
+    system_encoding = system_locale.split(".")[-1] if system_locale else "utf-8"
+
+    assert (
+        codecs.lookup(pd.options.display.encoding).name
+        == codecs.lookup(system_encoding).name
+    )

valley/lib/python3.10/site-packages/pandas/tests/copy_view/index/test_datetimeindex.py

@@ -0,0 +1,69 @@
+import pytest
+
+from pandas import (
+    DatetimeIndex,
+    Series,
+    Timestamp,
+    date_range,
+)
+import pandas._testing as tm
+
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Setting a value on a view:FutureWarning"
+)
+
+
+@pytest.mark.parametrize(
+    "cons",
+    [
+        lambda x: DatetimeIndex(x),
+        lambda x: DatetimeIndex(DatetimeIndex(x)),
+    ],
+)
+def test_datetimeindex(using_copy_on_write, cons):
+    dt = date_range("2019-12-31", periods=3, freq="D")
+    ser = Series(dt)
+    idx = cons(ser)
+    expected = idx.copy(deep=True)
+    ser.iloc[0] = Timestamp("2020-12-31")
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected)
+
+
+def test_datetimeindex_tz_convert(using_copy_on_write):
+    dt = date_range("2019-12-31", periods=3, freq="D", tz="Europe/Berlin")
+    ser = Series(dt)
+    idx = DatetimeIndex(ser).tz_convert("US/Eastern")
+    expected = idx.copy(deep=True)
+    ser.iloc[0] = Timestamp("2020-12-31", tz="Europe/Berlin")
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected)
+
+
+def test_datetimeindex_tz_localize(using_copy_on_write):
+    dt = date_range("2019-12-31", periods=3, freq="D")
+    ser = Series(dt)
+    idx = DatetimeIndex(ser).tz_localize("Europe/Berlin")
+    expected = idx.copy(deep=True)
+    ser.iloc[0] = Timestamp("2020-12-31")
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected)
+
+
+def test_datetimeindex_isocalendar(using_copy_on_write):
+    dt = date_range("2019-12-31", periods=3, freq="D")
+    ser = Series(dt)
+    df = DatetimeIndex(ser).isocalendar()
+    expected = df.index.copy(deep=True)
+    ser.iloc[0] = Timestamp("2020-12-31")
+    if using_copy_on_write:
+        tm.assert_index_equal(df.index, expected)
+
+
+def test_index_values(using_copy_on_write):
+    idx = date_range("2019-12-31", periods=3, freq="D")
+    result = idx.values
+    if using_copy_on_write:
+        assert result.flags.writeable is False
+    else:
+        assert result.flags.writeable is True

valley/lib/python3.10/site-packages/pandas/tests/copy_view/index/test_index.py

@@ -0,0 +1,184 @@
+import numpy as np
+import pytest
+
+from pandas import (
+    DataFrame,
+    Index,
+    Series,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+def index_view(index_data=[1, 2]):
+    df = DataFrame({"a": index_data, "b": 1.5})
+    view = df[:]
+    df = df.set_index("a", drop=True)
+    idx = df.index
+    # df = None
+    return idx, view
+
+
+def test_set_index_update_column(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": 1})
+    df = df.set_index("a", drop=False)
+    expected = df.index.copy(deep=True)
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 100
+    if using_copy_on_write:
+        tm.assert_index_equal(df.index, expected)
+    else:
+        tm.assert_index_equal(df.index, Index([100, 2], name="a"))
+
+
+def test_set_index_drop_update_column(using_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": 1.5})
+    view = df[:]
+    df = df.set_index("a", drop=True)
+    expected = df.index.copy(deep=True)
+    view.iloc[0, 0] = 100
+    tm.assert_index_equal(df.index, expected)
+
+
+def test_set_index_series(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": 1.5})
+    ser = Series([10, 11])
+    df = df.set_index(ser)
+    expected = df.index.copy(deep=True)
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser.iloc[0] = 100
+    if using_copy_on_write:
+        tm.assert_index_equal(df.index, expected)
+    else:
+        tm.assert_index_equal(df.index, Index([100, 11]))
+
+
+def test_assign_index_as_series(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": 1.5})
+    ser = Series([10, 11])
+    df.index = ser
+    expected = df.index.copy(deep=True)
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser.iloc[0] = 100
+    if using_copy_on_write:
+        tm.assert_index_equal(df.index, expected)
+    else:
+        tm.assert_index_equal(df.index, Index([100, 11]))
+
+
+def test_assign_index_as_index(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": 1.5})
+    ser = Series([10, 11])
+    rhs_index = Index(ser)
+    df.index = rhs_index
+    rhs_index = None  # overwrite to clear reference
+    expected = df.index.copy(deep=True)
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser.iloc[0] = 100
+    if using_copy_on_write:
+        tm.assert_index_equal(df.index, expected)
+    else:
+        tm.assert_index_equal(df.index, Index([100, 11]))
+
+
+def test_index_from_series(using_copy_on_write, warn_copy_on_write):
+    ser = Series([1, 2])
+    idx = Index(ser)
+    expected = idx.copy(deep=True)
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser.iloc[0] = 100
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected)
+    else:
+        tm.assert_index_equal(idx, Index([100, 2]))
+
+
+def test_index_from_series_copy(using_copy_on_write):
+    ser = Series([1, 2])
+    idx = Index(ser, copy=True)  # noqa: F841
+    arr = get_array(ser)
+    ser.iloc[0] = 100
+    assert np.shares_memory(get_array(ser), arr)
+
+
+def test_index_from_index(using_copy_on_write, warn_copy_on_write):
+    ser = Series([1, 2])
+    idx = Index(ser)
+    idx = Index(idx)
+    expected = idx.copy(deep=True)
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser.iloc[0] = 100
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected)
+    else:
+        tm.assert_index_equal(idx, Index([100, 2]))
+
+
+@pytest.mark.parametrize(
+    "func",
+    [
+        lambda x: x._shallow_copy(x._values),
+        lambda x: x.view(),
+        lambda x: x.take([0, 1]),
+        lambda x: x.repeat([1, 1]),
+        lambda x: x[slice(0, 2)],
+        lambda x: x[[0, 1]],
+        lambda x: x._getitem_slice(slice(0, 2)),
+        lambda x: x.delete([]),
+        lambda x: x.rename("b"),
+        lambda x: x.astype("Int64", copy=False),
+    ],
+    ids=[
+        "_shallow_copy",
+        "view",
+        "take",
+        "repeat",
+        "getitem_slice",
+        "getitem_list",
+        "_getitem_slice",
+        "delete",
+        "rename",
+        "astype",
+    ],
+)
+def test_index_ops(using_copy_on_write, func, request):
+    idx, view_ = index_view()
+    expected = idx.copy(deep=True)
+    if "astype" in request.node.callspec.id:
+        expected = expected.astype("Int64")
+    idx = func(idx)
+    view_.iloc[0, 0] = 100
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected, check_names=False)
+
+
+def test_infer_objects(using_copy_on_write):
+    idx, view_ = index_view(["a", "b"])
+    expected = idx.copy(deep=True)
+    idx = idx.infer_objects(copy=False)
+    view_.iloc[0, 0] = "aaaa"
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected, check_names=False)
+
+
+def test_index_to_frame(using_copy_on_write):
+    idx = Index([1, 2, 3], name="a")
+    expected = idx.copy(deep=True)
+    df = idx.to_frame()
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "a"), idx._values)
+        assert not df._mgr._has_no_reference(0)
+    else:
+        assert not np.shares_memory(get_array(df, "a"), idx._values)
+
+    df.iloc[0, 0] = 100
+    tm.assert_index_equal(idx, expected)
+
+
+def test_index_values(using_copy_on_write):
+    idx = Index([1, 2, 3])
+    result = idx.values
+    if using_copy_on_write:
+        assert result.flags.writeable is False
+    else:
+        assert result.flags.writeable is True

valley/lib/python3.10/site-packages/pandas/tests/copy_view/index/test_periodindex.py

@@ -0,0 +1,30 @@
+import pytest
+
+from pandas import (
+    Period,
+    PeriodIndex,
+    Series,
+    period_range,
+)
+import pandas._testing as tm
+
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Setting a value on a view:FutureWarning"
+)
+
+
+@pytest.mark.parametrize(
+    "cons",
+    [
+        lambda x: PeriodIndex(x),
+        lambda x: PeriodIndex(PeriodIndex(x)),
+    ],
+)
+def test_periodindex(using_copy_on_write, cons):
+    dt = period_range("2019-12-31", periods=3, freq="D")
+    ser = Series(dt)
+    idx = cons(ser)
+    expected = idx.copy(deep=True)
+    ser.iloc[0] = Period("2020-12-31")
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/index/test_timedeltaindex.py

@@ -0,0 +1,30 @@
+import pytest
+
+from pandas import (
+    Series,
+    Timedelta,
+    TimedeltaIndex,
+    timedelta_range,
+)
+import pandas._testing as tm
+
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:Setting a value on a view:FutureWarning"
+)
+
+
+@pytest.mark.parametrize(
+    "cons",
+    [
+        lambda x: TimedeltaIndex(x),
+        lambda x: TimedeltaIndex(TimedeltaIndex(x)),
+    ],
+)
+def test_timedeltaindex(using_copy_on_write, cons):
+    dt = timedelta_range("1 day", periods=3)
+    ser = Series(dt)
+    idx = cons(ser)
+    expected = idx.copy(deep=True)
+    ser.iloc[0] = Timedelta("5 days")
+    if using_copy_on_write:
+        tm.assert_index_equal(idx, expected)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_array.py

@@ -0,0 +1,190 @@
+import numpy as np
+import pytest
+
+from pandas import (
+    DataFrame,
+    Series,
+    date_range,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+# -----------------------------------------------------------------------------
+# Copy/view behaviour for accessing underlying array of Series/DataFrame
+
+
+@pytest.mark.parametrize(
+    "method",
+    [lambda ser: ser.values, lambda ser: np.asarray(ser)],
+    ids=["values", "asarray"],
+)
+def test_series_values(using_copy_on_write, method):
+    ser = Series([1, 2, 3], name="name")
+    ser_orig = ser.copy()
+
+    arr = method(ser)
+
+    if using_copy_on_write:
+        # .values still gives a view but is read-only
+        assert np.shares_memory(arr, get_array(ser, "name"))
+        assert arr.flags.writeable is False
+
+        # mutating series through arr therefore doesn't work
+        with pytest.raises(ValueError, match="read-only"):
+            arr[0] = 0
+        tm.assert_series_equal(ser, ser_orig)
+
+        # mutating the series itself still works
+        ser.iloc[0] = 0
+        assert ser.values[0] == 0
+    else:
+        assert arr.flags.writeable is True
+        arr[0] = 0
+        assert ser.iloc[0] == 0
+
+
+@pytest.mark.parametrize(
+    "method",
+    [lambda df: df.values, lambda df: np.asarray(df)],
+    ids=["values", "asarray"],
+)
+def test_dataframe_values(using_copy_on_write, using_array_manager, method):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    df_orig = df.copy()
+
+    arr = method(df)
+
+    if using_copy_on_write:
+        # .values still gives a view but is read-only
+        assert np.shares_memory(arr, get_array(df, "a"))
+        assert arr.flags.writeable is False
+
+        # mutating series through arr therefore doesn't work
+        with pytest.raises(ValueError, match="read-only"):
+            arr[0, 0] = 0
+        tm.assert_frame_equal(df, df_orig)
+
+        # mutating the series itself still works
+        df.iloc[0, 0] = 0
+        assert df.values[0, 0] == 0
+    else:
+        assert arr.flags.writeable is True
+        arr[0, 0] = 0
+        if not using_array_manager:
+            assert df.iloc[0, 0] == 0
+        else:
+            tm.assert_frame_equal(df, df_orig)
+
+
+def test_series_to_numpy(using_copy_on_write):
+    ser = Series([1, 2, 3], name="name")
+    ser_orig = ser.copy()
+
+    # default: copy=False, no dtype or NAs
+    arr = ser.to_numpy()
+    if using_copy_on_write:
+        # to_numpy still gives a view but is read-only
+        assert np.shares_memory(arr, get_array(ser, "name"))
+        assert arr.flags.writeable is False
+
+        # mutating series through arr therefore doesn't work
+        with pytest.raises(ValueError, match="read-only"):
+            arr[0] = 0
+        tm.assert_series_equal(ser, ser_orig)
+
+        # mutating the series itself still works
+        ser.iloc[0] = 0
+        assert ser.values[0] == 0
+    else:
+        assert arr.flags.writeable is True
+        arr[0] = 0
+        assert ser.iloc[0] == 0
+
+    # specify copy=False gives a writeable array
+    ser = Series([1, 2, 3], name="name")
+    arr = ser.to_numpy(copy=True)
+    assert not np.shares_memory(arr, get_array(ser, "name"))
+    assert arr.flags.writeable is True
+
+    # specifying a dtype that already causes a copy also gives a writeable array
+    ser = Series([1, 2, 3], name="name")
+    arr = ser.to_numpy(dtype="float64")
+    assert not np.shares_memory(arr, get_array(ser, "name"))
+    assert arr.flags.writeable is True
+
+
+@pytest.mark.parametrize("order", ["F", "C"])
+def test_ravel_read_only(using_copy_on_write, order):
+    ser = Series([1, 2, 3])
+    with tm.assert_produces_warning(FutureWarning, match="is deprecated"):
+        arr = ser.ravel(order=order)
+    if using_copy_on_write:
+        assert arr.flags.writeable is False
+    assert np.shares_memory(get_array(ser), arr)
+
+
+def test_series_array_ea_dtypes(using_copy_on_write):
+    ser = Series([1, 2, 3], dtype="Int64")
+    arr = np.asarray(ser, dtype="int64")
+    assert np.shares_memory(arr, get_array(ser))
+    if using_copy_on_write:
+        assert arr.flags.writeable is False
+    else:
+        assert arr.flags.writeable is True
+
+    arr = np.asarray(ser)
+    assert np.shares_memory(arr, get_array(ser))
+    if using_copy_on_write:
+        assert arr.flags.writeable is False
+    else:
+        assert arr.flags.writeable is True
+
+
+def test_dataframe_array_ea_dtypes(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]}, dtype="Int64")
+    arr = np.asarray(df, dtype="int64")
+    assert np.shares_memory(arr, get_array(df, "a"))
+    if using_copy_on_write:
+        assert arr.flags.writeable is False
+    else:
+        assert arr.flags.writeable is True
+
+    arr = np.asarray(df)
+    assert np.shares_memory(arr, get_array(df, "a"))
+    if using_copy_on_write:
+        assert arr.flags.writeable is False
+    else:
+        assert arr.flags.writeable is True
+
+
+def test_dataframe_array_string_dtype(using_copy_on_write, using_array_manager):
+    df = DataFrame({"a": ["a", "b"]}, dtype="string")
+    arr = np.asarray(df)
+    if not using_array_manager:
+        assert np.shares_memory(arr, get_array(df, "a"))
+    if using_copy_on_write:
+        assert arr.flags.writeable is False
+    else:
+        assert arr.flags.writeable is True
+
+
+def test_dataframe_multiple_numpy_dtypes():
+    df = DataFrame({"a": [1, 2, 3], "b": 1.5})
+    arr = np.asarray(df)
+    assert not np.shares_memory(arr, get_array(df, "a"))
+    assert arr.flags.writeable is True
+
+
+def test_values_is_ea(using_copy_on_write):
+    df = DataFrame({"a": date_range("2012-01-01", periods=3)})
+    arr = np.asarray(df)
+    if using_copy_on_write:
+        assert arr.flags.writeable is False
+    else:
+        assert arr.flags.writeable is True
+
+
+def test_empty_dataframe():
+    df = DataFrame()
+    arr = np.asarray(df)
+    assert arr.flags.writeable is True

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_astype.py

@@ -0,0 +1,260 @@
+import pickle
+
+import numpy as np
+import pytest
+
+from pandas.compat.pyarrow import pa_version_under12p0
+import pandas.util._test_decorators as td
+
+import pandas as pd
+from pandas import (
+    DataFrame,
+    Series,
+    Timestamp,
+    date_range,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+def test_astype_single_dtype(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": 1.5})
+    df_orig = df.copy()
+    df2 = df.astype("float64")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column/block
+    df2.iloc[0, 2] = 5.5
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    tm.assert_frame_equal(df, df_orig)
+
+    # mutating parent also doesn't update result
+    df2 = df.astype("float64")
+    df.iloc[0, 2] = 5.5
+    tm.assert_frame_equal(df2, df_orig.astype("float64"))
+
+
+@pytest.mark.parametrize("dtype", ["int64", "Int64"])
+@pytest.mark.parametrize("new_dtype", ["int64", "Int64", "int64[pyarrow]"])
+def test_astype_avoids_copy(using_copy_on_write, dtype, new_dtype):
+    if new_dtype == "int64[pyarrow]":
+        pytest.importorskip("pyarrow")
+    df = DataFrame({"a": [1, 2, 3]}, dtype=dtype)
+    df_orig = df.copy()
+    df2 = df.astype(new_dtype)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column/block
+    df2.iloc[0, 0] = 10
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+    # mutating parent also doesn't update result
+    df2 = df.astype(new_dtype)
+    df.iloc[0, 0] = 100
+    tm.assert_frame_equal(df2, df_orig.astype(new_dtype))
+
+
+@pytest.mark.parametrize("dtype", ["float64", "int32", "Int32", "int32[pyarrow]"])
+def test_astype_different_target_dtype(using_copy_on_write, dtype):
+    if dtype == "int32[pyarrow]":
+        pytest.importorskip("pyarrow")
+    df = DataFrame({"a": [1, 2, 3]})
+    df_orig = df.copy()
+    df2 = df.astype(dtype)
+
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert df2._mgr._has_no_reference(0)
+
+    df2.iloc[0, 0] = 5
+    tm.assert_frame_equal(df, df_orig)
+
+    # mutating parent also doesn't update result
+    df2 = df.astype(dtype)
+    df.iloc[0, 0] = 100
+    tm.assert_frame_equal(df2, df_orig.astype(dtype))
+
+
+@td.skip_array_manager_invalid_test
+def test_astype_numpy_to_ea():
+    ser = Series([1, 2, 3])
+    with pd.option_context("mode.copy_on_write", True):
+        result = ser.astype("Int64")
+    assert np.shares_memory(get_array(ser), get_array(result))
+
+
+@pytest.mark.parametrize(
+    "dtype, new_dtype", [("object", "string"), ("string", "object")]
+)
+def test_astype_string_and_object(using_copy_on_write, dtype, new_dtype):
+    df = DataFrame({"a": ["a", "b", "c"]}, dtype=dtype)
+    df_orig = df.copy()
+    df2 = df.astype(new_dtype)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 0] = "x"
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "dtype, new_dtype", [("object", "string"), ("string", "object")]
+)
+def test_astype_string_and_object_update_original(
+    using_copy_on_write, dtype, new_dtype
+):
+    df = DataFrame({"a": ["a", "b", "c"]}, dtype=dtype)
+    df2 = df.astype(new_dtype)
+    df_orig = df2.copy()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df.iloc[0, 0] = "x"
+    tm.assert_frame_equal(df2, df_orig)
+
+
+def test_astype_string_copy_on_pickle_roundrip():
+    # https://github.com/pandas-dev/pandas/issues/54654
+    # ensure_string_array may alter array inplace
+    base = Series(np.array([(1, 2), None, 1], dtype="object"))
+    base_copy = pickle.loads(pickle.dumps(base))
+    base_copy.astype(str)
+    tm.assert_series_equal(base, base_copy)
+
+
+def test_astype_dict_dtypes(using_copy_on_write):
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": Series([1.5, 1.5, 1.5], dtype="float64")}
+    )
+    df_orig = df.copy()
+    df2 = df.astype({"a": "float64", "c": "float64"})
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column/block
+    df2.iloc[0, 2] = 5.5
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+
+    df2.iloc[0, 1] = 10
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_astype_different_datetime_resos(using_copy_on_write):
+    df = DataFrame({"a": date_range("2019-12-31", periods=2, freq="D")})
+    result = df.astype("datetime64[ms]")
+
+    assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+    if using_copy_on_write:
+        assert result._mgr._has_no_reference(0)
+
+
+def test_astype_different_timezones(using_copy_on_write):
+    df = DataFrame(
+        {"a": date_range("2019-12-31", periods=5, freq="D", tz="US/Pacific")}
+    )
+    result = df.astype("datetime64[ns, Europe/Berlin]")
+    if using_copy_on_write:
+        assert not result._mgr._has_no_reference(0)
+        assert np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+
+
+def test_astype_different_timezones_different_reso(using_copy_on_write):
+    df = DataFrame(
+        {"a": date_range("2019-12-31", periods=5, freq="D", tz="US/Pacific")}
+    )
+    result = df.astype("datetime64[ms, Europe/Berlin]")
+    if using_copy_on_write:
+        assert result._mgr._has_no_reference(0)
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+
+
+def test_astype_arrow_timestamp(using_copy_on_write):
+    pytest.importorskip("pyarrow")
+    df = DataFrame(
+        {
+            "a": [
+                Timestamp("2020-01-01 01:01:01.000001"),
+                Timestamp("2020-01-01 01:01:01.000001"),
+            ]
+        },
+        dtype="M8[ns]",
+    )
+    result = df.astype("timestamp[ns][pyarrow]")
+    if using_copy_on_write:
+        assert not result._mgr._has_no_reference(0)
+        if pa_version_under12p0:
+            assert not np.shares_memory(
+                get_array(df, "a"), get_array(result, "a")._pa_array
+            )
+        else:
+            assert np.shares_memory(
+                get_array(df, "a"), get_array(result, "a")._pa_array
+            )
+
+
+def test_convert_dtypes_infer_objects(using_copy_on_write):
+    ser = Series(["a", "b", "c"])
+    ser_orig = ser.copy()
+    result = ser.convert_dtypes(
+        convert_integer=False,
+        convert_boolean=False,
+        convert_floating=False,
+        convert_string=False,
+    )
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(ser), get_array(result))
+    else:
+        assert not np.shares_memory(get_array(ser), get_array(result))
+
+    result.iloc[0] = "x"
+    tm.assert_series_equal(ser, ser_orig)
+
+
+def test_convert_dtypes(using_copy_on_write):
+    df = DataFrame({"a": ["a", "b"], "b": [1, 2], "c": [1.5, 2.5], "d": [True, False]})
+    df_orig = df.copy()
+    df2 = df.convert_dtypes()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+        assert np.shares_memory(get_array(df2, "d"), get_array(df, "d"))
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+        assert not np.shares_memory(get_array(df2, "d"), get_array(df, "d"))
+
+    df2.iloc[0, 0] = "x"
+    tm.assert_frame_equal(df, df_orig)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_chained_assignment_deprecation.py

@@ -0,0 +1,174 @@
+import numpy as np
+import pytest
+
+from pandas.compat import PY311
+from pandas.errors import (
+    ChainedAssignmentError,
+    SettingWithCopyWarning,
+)
+
+from pandas import (
+    DataFrame,
+    option_context,
+)
+import pandas._testing as tm
+
+
+def test_methods_iloc_warn(using_copy_on_write):
+    if not using_copy_on_write:
+        df = DataFrame({"a": [1, 2, 3], "b": 1})
+        with tm.assert_cow_warning(match="A value"):
+            df.iloc[:, 0].replace(1, 5, inplace=True)
+
+        with tm.assert_cow_warning(match="A value"):
+            df.iloc[:, 0].fillna(1, inplace=True)
+
+        with tm.assert_cow_warning(match="A value"):
+            df.iloc[:, 0].interpolate(inplace=True)
+
+        with tm.assert_cow_warning(match="A value"):
+            df.iloc[:, 0].ffill(inplace=True)
+
+        with tm.assert_cow_warning(match="A value"):
+            df.iloc[:, 0].bfill(inplace=True)
+
+
+@pytest.mark.parametrize(
+    "func, args",
+    [
+        ("replace", (4, 5)),
+        ("fillna", (1,)),
+        ("interpolate", ()),
+        ("bfill", ()),
+        ("ffill", ()),
+    ],
+)
+def test_methods_iloc_getitem_item_cache(
+    func, args, using_copy_on_write, warn_copy_on_write
+):
+    # ensure we don't incorrectly raise chained assignment warning because
+    # of the item cache / iloc not setting the item cache
+    df_orig = DataFrame({"a": [1, 2, 3], "b": 1})
+
+    df = df_orig.copy()
+    ser = df.iloc[:, 0]
+    getattr(ser, func)(*args, inplace=True)
+
+    # parent that holds item_cache is dead, so don't increase ref count
+    df = df_orig.copy()
+    ser = df.copy()["a"]
+    getattr(ser, func)(*args, inplace=True)
+
+    df = df_orig.copy()
+    df["a"]  # populate the item_cache
+    ser = df.iloc[:, 0]  # iloc creates a new object
+    getattr(ser, func)(*args, inplace=True)
+
+    df = df_orig.copy()
+    df["a"]  # populate the item_cache
+    ser = df["a"]
+    getattr(ser, func)(*args, inplace=True)
+
+    df = df_orig.copy()
+    df["a"]  # populate the item_cache
+    # TODO(CoW-warn) because of the usage of *args, this doesn't warn on Py3.11+
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error(not PY311):
+            getattr(df["a"], func)(*args, inplace=True)
+    else:
+        with tm.assert_cow_warning(not PY311, match="A value"):
+            getattr(df["a"], func)(*args, inplace=True)
+
+    df = df_orig.copy()
+    ser = df["a"]  # populate the item_cache and keep ref
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error(not PY311):
+            getattr(df["a"], func)(*args, inplace=True)
+    else:
+        # ideally also warns on the default mode, but the ser' _cacher
+        # messes up the refcount + even in warning mode this doesn't trigger
+        # the warning of Py3.1+ (see above)
+        with tm.assert_cow_warning(warn_copy_on_write and not PY311, match="A value"):
+            getattr(df["a"], func)(*args, inplace=True)
+
+
+def test_methods_iloc_getitem_item_cache_fillna(
+    using_copy_on_write, warn_copy_on_write
+):
+    # ensure we don't incorrectly raise chained assignment warning because
+    # of the item cache / iloc not setting the item cache
+    df_orig = DataFrame({"a": [1, 2, 3], "b": 1})
+
+    df = df_orig.copy()
+    ser = df.iloc[:, 0]
+    ser.fillna(1, inplace=True)
+
+    # parent that holds item_cache is dead, so don't increase ref count
+    df = df_orig.copy()
+    ser = df.copy()["a"]
+    ser.fillna(1, inplace=True)
+
+    df = df_orig.copy()
+    df["a"]  # populate the item_cache
+    ser = df.iloc[:, 0]  # iloc creates a new object
+    ser.fillna(1, inplace=True)
+
+    df = df_orig.copy()
+    df["a"]  # populate the item_cache
+    ser = df["a"]
+    ser.fillna(1, inplace=True)
+
+    df = df_orig.copy()
+    df["a"]  # populate the item_cache
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error():
+            df["a"].fillna(1, inplace=True)
+    else:
+        with tm.assert_cow_warning(match="A value"):
+            df["a"].fillna(1, inplace=True)
+
+    df = df_orig.copy()
+    ser = df["a"]  # populate the item_cache and keep ref
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error():
+            df["a"].fillna(1, inplace=True)
+    else:
+        # TODO(CoW-warn) ideally also warns on the default mode, but the ser' _cacher
+        # messes up the refcount
+        with tm.assert_cow_warning(warn_copy_on_write, match="A value"):
+            df["a"].fillna(1, inplace=True)
+
+
+# TODO(CoW-warn) expand the cases
+@pytest.mark.parametrize(
+    "indexer", [0, [0, 1], slice(0, 2), np.array([True, False, True])]
+)
+def test_series_setitem(indexer, using_copy_on_write, warn_copy_on_write):
+    # ensure we only get a single warning for those typical cases of chained
+    # assignment
+    df = DataFrame({"a": [1, 2, 3], "b": 1})
+
+    # using custom check instead of tm.assert_produces_warning because that doesn't
+    # fail if multiple warnings are raised
+    with pytest.warns() as record:
+        df["a"][indexer] = 0
+    assert len(record) == 1
+    if using_copy_on_write:
+        assert record[0].category == ChainedAssignmentError
+    else:
+        assert record[0].category == FutureWarning
+        assert "ChainedAssignmentError" in record[0].message.args[0]
+
+
+@pytest.mark.filterwarnings("ignore::pandas.errors.SettingWithCopyWarning")
+@pytest.mark.parametrize(
+    "indexer", ["a", ["a", "b"], slice(0, 2), np.array([True, False, True])]
+)
+def test_frame_setitem(indexer, using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3, 4, 5], "b": 1})
+
+    extra_warnings = () if using_copy_on_write else (SettingWithCopyWarning,)
+
+    with option_context("chained_assignment", "warn"):
+        with tm.raises_chained_assignment_error(extra_warnings=extra_warnings):
+            df[0:3][indexer] = 10

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_clip.py

@@ -0,0 +1,101 @@
+import numpy as np
+
+from pandas import (
+    DataFrame,
+    option_context,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+def test_clip_inplace_reference(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    df_copy = df.copy()
+    arr_a = get_array(df, "a")
+    view = df[:]
+    if warn_copy_on_write:
+        with tm.assert_cow_warning():
+            df.clip(lower=2, inplace=True)
+    else:
+        df.clip(lower=2, inplace=True)
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), arr_a)
+        assert df._mgr._has_no_reference(0)
+        assert view._mgr._has_no_reference(0)
+        tm.assert_frame_equal(df_copy, view)
+    else:
+        assert np.shares_memory(get_array(df, "a"), arr_a)
+
+
+def test_clip_inplace_reference_no_op(using_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    df_copy = df.copy()
+    arr_a = get_array(df, "a")
+    view = df[:]
+    df.clip(lower=0, inplace=True)
+
+    assert np.shares_memory(get_array(df, "a"), arr_a)
+
+    if using_copy_on_write:
+        assert not df._mgr._has_no_reference(0)
+        assert not view._mgr._has_no_reference(0)
+        tm.assert_frame_equal(df_copy, view)
+
+
+def test_clip_inplace(using_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    arr_a = get_array(df, "a")
+    df.clip(lower=2, inplace=True)
+
+    assert np.shares_memory(get_array(df, "a"), arr_a)
+
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+
+
+def test_clip(using_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    df_orig = df.copy()
+    df2 = df.clip(lower=2)
+
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+    tm.assert_frame_equal(df_orig, df)
+
+
+def test_clip_no_op(using_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    df2 = df.clip(lower=0)
+
+    if using_copy_on_write:
+        assert not df._mgr._has_no_reference(0)
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+
+def test_clip_chained_inplace(using_copy_on_write):
+    df = DataFrame({"a": [1, 4, 2], "b": 1})
+    df_orig = df.copy()
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error():
+            df["a"].clip(1, 2, inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+
+        with tm.raises_chained_assignment_error():
+            df[["a"]].clip(1, 2, inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+            df["a"].clip(1, 2, inplace=True)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                df[["a"]].clip(1, 2, inplace=True)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                df[df["a"] > 1].clip(1, 2, inplace=True)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_constructors.py

@@ -0,0 +1,382 @@
+import numpy as np
+import pytest
+
+import pandas as pd
+from pandas import (
+    DataFrame,
+    DatetimeIndex,
+    Index,
+    Period,
+    PeriodIndex,
+    Series,
+    Timedelta,
+    TimedeltaIndex,
+    Timestamp,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+# -----------------------------------------------------------------------------
+# Copy/view behaviour for Series / DataFrame constructors
+
+
+@pytest.mark.parametrize("dtype", [None, "int64"])
+def test_series_from_series(dtype, using_copy_on_write, warn_copy_on_write):
+    # Case: constructing a Series from another Series object follows CoW rules:
+    # a new object is returned and thus mutations are not propagated
+    ser = Series([1, 2, 3], name="name")
+
+    # default is copy=False -> new Series is a shallow copy / view of original
+    result = Series(ser, dtype=dtype)
+
+    # the shallow copy still shares memory
+    assert np.shares_memory(get_array(ser), get_array(result))
+
+    if using_copy_on_write:
+        assert result._mgr.blocks[0].refs.has_reference()
+
+    if using_copy_on_write:
+        # mutating new series copy doesn't mutate original
+        result.iloc[0] = 0
+        assert ser.iloc[0] == 1
+        # mutating triggered a copy-on-write -> no longer shares memory
+        assert not np.shares_memory(get_array(ser), get_array(result))
+    else:
+        # mutating shallow copy does mutate original
+        with tm.assert_cow_warning(warn_copy_on_write):
+            result.iloc[0] = 0
+        assert ser.iloc[0] == 0
+        # and still shares memory
+        assert np.shares_memory(get_array(ser), get_array(result))
+
+    # the same when modifying the parent
+    result = Series(ser, dtype=dtype)
+
+    if using_copy_on_write:
+        # mutating original doesn't mutate new series
+        ser.iloc[0] = 0
+        assert result.iloc[0] == 1
+    else:
+        # mutating original does mutate shallow copy
+        with tm.assert_cow_warning(warn_copy_on_write):
+            ser.iloc[0] = 0
+        assert result.iloc[0] == 0
+
+
+def test_series_from_series_with_reindex(using_copy_on_write, warn_copy_on_write):
+    # Case: constructing a Series from another Series with specifying an index
+    # that potentially requires a reindex of the values
+    ser = Series([1, 2, 3], name="name")
+
+    # passing an index that doesn't actually require a reindex of the values
+    # -> without CoW we get an actual mutating view
+    for index in [
+        ser.index,
+        ser.index.copy(),
+        list(ser.index),
+        ser.index.rename("idx"),
+    ]:
+        result = Series(ser, index=index)
+        assert np.shares_memory(ser.values, result.values)
+        with tm.assert_cow_warning(warn_copy_on_write):
+            result.iloc[0] = 0
+        if using_copy_on_write:
+            assert ser.iloc[0] == 1
+        else:
+            assert ser.iloc[0] == 0
+
+    # ensure that if an actual reindex is needed, we don't have any refs
+    # (mutating the result wouldn't trigger CoW)
+    result = Series(ser, index=[0, 1, 2, 3])
+    assert not np.shares_memory(ser.values, result.values)
+    if using_copy_on_write:
+        assert not result._mgr.blocks[0].refs.has_reference()
+
+
+@pytest.mark.parametrize("fastpath", [False, True])
+@pytest.mark.parametrize("dtype", [None, "int64"])
+@pytest.mark.parametrize("idx", [None, pd.RangeIndex(start=0, stop=3, step=1)])
+@pytest.mark.parametrize(
+    "arr", [np.array([1, 2, 3], dtype="int64"), pd.array([1, 2, 3], dtype="Int64")]
+)
+def test_series_from_array(using_copy_on_write, idx, dtype, fastpath, arr):
+    if idx is None or dtype is not None:
+        fastpath = False
+    msg = "The 'fastpath' keyword in pd.Series is deprecated"
+    with tm.assert_produces_warning(DeprecationWarning, match=msg):
+        ser = Series(arr, dtype=dtype, index=idx, fastpath=fastpath)
+    ser_orig = ser.copy()
+    data = getattr(arr, "_data", arr)
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(ser), data)
+    else:
+        assert np.shares_memory(get_array(ser), data)
+
+    arr[0] = 100
+    if using_copy_on_write:
+        tm.assert_series_equal(ser, ser_orig)
+    else:
+        expected = Series([100, 2, 3], dtype=dtype if dtype is not None else arr.dtype)
+        tm.assert_series_equal(ser, expected)
+
+
+@pytest.mark.parametrize("copy", [True, False, None])
+def test_series_from_array_different_dtype(using_copy_on_write, copy):
+    arr = np.array([1, 2, 3], dtype="int64")
+    ser = Series(arr, dtype="int32", copy=copy)
+    assert not np.shares_memory(get_array(ser), arr)
+
+
+@pytest.mark.parametrize(
+    "idx",
+    [
+        Index([1, 2]),
+        DatetimeIndex([Timestamp("2019-12-31"), Timestamp("2020-12-31")]),
+        PeriodIndex([Period("2019-12-31"), Period("2020-12-31")]),
+        TimedeltaIndex([Timedelta("1 days"), Timedelta("2 days")]),
+    ],
+)
+def test_series_from_index(using_copy_on_write, idx):
+    ser = Series(idx)
+    expected = idx.copy(deep=True)
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(ser), get_array(idx))
+        assert not ser._mgr._has_no_reference(0)
+    else:
+        assert not np.shares_memory(get_array(ser), get_array(idx))
+    ser.iloc[0] = ser.iloc[1]
+    tm.assert_index_equal(idx, expected)
+
+
+def test_series_from_index_different_dtypes(using_copy_on_write):
+    idx = Index([1, 2, 3], dtype="int64")
+    ser = Series(idx, dtype="int32")
+    assert not np.shares_memory(get_array(ser), get_array(idx))
+    if using_copy_on_write:
+        assert ser._mgr._has_no_reference(0)
+
+
+@pytest.mark.filterwarnings("ignore:Setting a value on a view:FutureWarning")
+@pytest.mark.parametrize("fastpath", [False, True])
+@pytest.mark.parametrize("dtype", [None, "int64"])
+@pytest.mark.parametrize("idx", [None, pd.RangeIndex(start=0, stop=3, step=1)])
+def test_series_from_block_manager(using_copy_on_write, idx, dtype, fastpath):
+    ser = Series([1, 2, 3], dtype="int64")
+    ser_orig = ser.copy()
+    msg = "The 'fastpath' keyword in pd.Series is deprecated"
+    with tm.assert_produces_warning(DeprecationWarning, match=msg):
+        ser2 = Series(ser._mgr, dtype=dtype, fastpath=fastpath, index=idx)
+    assert np.shares_memory(get_array(ser), get_array(ser2))
+    if using_copy_on_write:
+        assert not ser2._mgr._has_no_reference(0)
+
+    ser2.iloc[0] = 100
+    if using_copy_on_write:
+        tm.assert_series_equal(ser, ser_orig)
+    else:
+        expected = Series([100, 2, 3])
+        tm.assert_series_equal(ser, expected)
+
+
+def test_series_from_block_manager_different_dtype(using_copy_on_write):
+    ser = Series([1, 2, 3], dtype="int64")
+    msg = "Passing a SingleBlockManager to Series"
+    with tm.assert_produces_warning(DeprecationWarning, match=msg):
+        ser2 = Series(ser._mgr, dtype="int32")
+    assert not np.shares_memory(get_array(ser), get_array(ser2))
+    if using_copy_on_write:
+        assert ser2._mgr._has_no_reference(0)
+
+
+@pytest.mark.parametrize("use_mgr", [True, False])
+@pytest.mark.parametrize("columns", [None, ["a"]])
+def test_dataframe_constructor_mgr_or_df(
+    using_copy_on_write, warn_copy_on_write, columns, use_mgr
+):
+    df = DataFrame({"a": [1, 2, 3]})
+    df_orig = df.copy()
+
+    if use_mgr:
+        data = df._mgr
+        warn = DeprecationWarning
+    else:
+        data = df
+        warn = None
+    msg = "Passing a BlockManager to DataFrame"
+    with tm.assert_produces_warning(warn, match=msg, check_stacklevel=False):
+        new_df = DataFrame(data)
+
+    assert np.shares_memory(get_array(df, "a"), get_array(new_df, "a"))
+    with tm.assert_cow_warning(warn_copy_on_write and not use_mgr):
+        new_df.iloc[0] = 100
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), get_array(new_df, "a"))
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert np.shares_memory(get_array(df, "a"), get_array(new_df, "a"))
+        tm.assert_frame_equal(df, new_df)
+
+
+@pytest.mark.parametrize("dtype", [None, "int64", "Int64"])
+@pytest.mark.parametrize("index", [None, [0, 1, 2]])
+@pytest.mark.parametrize("columns", [None, ["a", "b"], ["a", "b", "c"]])
+def test_dataframe_from_dict_of_series(
+    request, using_copy_on_write, warn_copy_on_write, columns, index, dtype
+):
+    # Case: constructing a DataFrame from Series objects with copy=False
+    # has to do a lazy following CoW rules
+    # (the default for DataFrame(dict) is still to copy to ensure consolidation)
+    s1 = Series([1, 2, 3])
+    s2 = Series([4, 5, 6])
+    s1_orig = s1.copy()
+    expected = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6]}, index=index, columns=columns, dtype=dtype
+    )
+
+    result = DataFrame(
+        {"a": s1, "b": s2}, index=index, columns=columns, dtype=dtype, copy=False
+    )
+
+    # the shallow copy still shares memory
+    assert np.shares_memory(get_array(result, "a"), get_array(s1))
+
+    # mutating the new dataframe doesn't mutate original
+    with tm.assert_cow_warning(warn_copy_on_write):
+        result.iloc[0, 0] = 10
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(s1))
+        tm.assert_series_equal(s1, s1_orig)
+    else:
+        assert s1.iloc[0] == 10
+
+    # the same when modifying the parent series
+    s1 = Series([1, 2, 3])
+    s2 = Series([4, 5, 6])
+    result = DataFrame(
+        {"a": s1, "b": s2}, index=index, columns=columns, dtype=dtype, copy=False
+    )
+    with tm.assert_cow_warning(warn_copy_on_write):
+        s1.iloc[0] = 10
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(s1))
+        tm.assert_frame_equal(result, expected)
+    else:
+        assert result.iloc[0, 0] == 10
+
+
+@pytest.mark.parametrize("dtype", [None, "int64"])
+def test_dataframe_from_dict_of_series_with_reindex(dtype):
+    # Case: constructing a DataFrame from Series objects with copy=False
+    # and passing an index that requires an actual (no-view) reindex -> need
+    # to ensure the result doesn't have refs set up to unnecessarily trigger
+    # a copy on write
+    s1 = Series([1, 2, 3])
+    s2 = Series([4, 5, 6])
+    df = DataFrame({"a": s1, "b": s2}, index=[1, 2, 3], dtype=dtype, copy=False)
+
+    # df should own its memory, so mutating shouldn't trigger a copy
+    arr_before = get_array(df, "a")
+    assert not np.shares_memory(arr_before, get_array(s1))
+    df.iloc[0, 0] = 100
+    arr_after = get_array(df, "a")
+    assert np.shares_memory(arr_before, arr_after)
+
+
+@pytest.mark.parametrize("cons", [Series, Index])
+@pytest.mark.parametrize(
+    "data, dtype", [([1, 2], None), ([1, 2], "int64"), (["a", "b"], None)]
+)
+def test_dataframe_from_series_or_index(
+    using_copy_on_write, warn_copy_on_write, data, dtype, cons
+):
+    obj = cons(data, dtype=dtype)
+    obj_orig = obj.copy()
+    df = DataFrame(obj, dtype=dtype)
+    assert np.shares_memory(get_array(obj), get_array(df, 0))
+    if using_copy_on_write:
+        assert not df._mgr._has_no_reference(0)
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = data[-1]
+    if using_copy_on_write:
+        tm.assert_equal(obj, obj_orig)
+
+
+@pytest.mark.parametrize("cons", [Series, Index])
+def test_dataframe_from_series_or_index_different_dtype(using_copy_on_write, cons):
+    obj = cons([1, 2], dtype="int64")
+    df = DataFrame(obj, dtype="int32")
+    assert not np.shares_memory(get_array(obj), get_array(df, 0))
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+
+
+def test_dataframe_from_series_infer_datetime(using_copy_on_write):
+    ser = Series([Timestamp("2019-12-31"), Timestamp("2020-12-31")], dtype=object)
+    with tm.assert_produces_warning(FutureWarning, match="Dtype inference"):
+        df = DataFrame(ser)
+    assert not np.shares_memory(get_array(ser), get_array(df, 0))
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+
+
+@pytest.mark.parametrize("index", [None, [0, 1, 2]])
+def test_dataframe_from_dict_of_series_with_dtype(index):
+    # Variant of above, but now passing a dtype that causes a copy
+    # -> need to ensure the result doesn't have refs set up to unnecessarily
+    # trigger a copy on write
+    s1 = Series([1.0, 2.0, 3.0])
+    s2 = Series([4, 5, 6])
+    df = DataFrame({"a": s1, "b": s2}, index=index, dtype="int64", copy=False)
+
+    # df should own its memory, so mutating shouldn't trigger a copy
+    arr_before = get_array(df, "a")
+    assert not np.shares_memory(arr_before, get_array(s1))
+    df.iloc[0, 0] = 100
+    arr_after = get_array(df, "a")
+    assert np.shares_memory(arr_before, arr_after)
+
+
+@pytest.mark.parametrize("copy", [False, None, True])
+def test_frame_from_numpy_array(using_copy_on_write, copy, using_array_manager):
+    arr = np.array([[1, 2], [3, 4]])
+    df = DataFrame(arr, copy=copy)
+
+    if (
+        using_copy_on_write
+        and copy is not False
+        or copy is True
+        or (using_array_manager and copy is None)
+    ):
+        assert not np.shares_memory(get_array(df, 0), arr)
+    else:
+        assert np.shares_memory(get_array(df, 0), arr)
+
+
+def test_dataframe_from_records_with_dataframe(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]})
+    df_orig = df.copy()
+    with tm.assert_produces_warning(FutureWarning):
+        df2 = DataFrame.from_records(df)
+    if using_copy_on_write:
+        assert not df._mgr._has_no_reference(0)
+    assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df2.iloc[0, 0] = 100
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        tm.assert_frame_equal(df, df2)
+
+
+def test_frame_from_dict_of_index(using_copy_on_write):
+    idx = Index([1, 2, 3])
+    expected = idx.copy(deep=True)
+    df = DataFrame({"a": idx}, copy=False)
+    assert np.shares_memory(get_array(df, "a"), idx._values)
+    if using_copy_on_write:
+        assert not df._mgr._has_no_reference(0)
+
+        df.iloc[0, 0] = 100
+        tm.assert_index_equal(idx, expected)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_core_functionalities.py

@@ -0,0 +1,106 @@
+import numpy as np
+import pytest
+
+from pandas import DataFrame
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+def test_assigning_to_same_variable_removes_references(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]})
+    df = df.reset_index()
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(1)
+    arr = get_array(df, "a")
+    df.iloc[0, 1] = 100  # Write into a
+
+    assert np.shares_memory(arr, get_array(df, "a"))
+
+
+def test_setitem_dont_track_unnecessary_references(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1, "c": 1})
+
+    df["b"] = 100
+    arr = get_array(df, "a")
+    # We split the block in setitem, if we are not careful the new blocks will
+    # reference each other triggering a copy
+    df.iloc[0, 0] = 100
+    assert np.shares_memory(arr, get_array(df, "a"))
+
+
+def test_setitem_with_view_copies(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1, "c": 1})
+    view = df[:]
+    expected = df.copy()
+
+    df["b"] = 100
+    arr = get_array(df, "a")
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 100  # Check that we correctly track reference
+    if using_copy_on_write:
+        assert not np.shares_memory(arr, get_array(df, "a"))
+        tm.assert_frame_equal(view, expected)
+
+
+def test_setitem_with_view_invalidated_does_not_copy(
+    using_copy_on_write, warn_copy_on_write, request
+):
+    df = DataFrame({"a": [1, 2, 3], "b": 1, "c": 1})
+    view = df[:]
+
+    df["b"] = 100
+    arr = get_array(df, "a")
+    view = None  # noqa: F841
+    # TODO(CoW-warn) false positive? -> block gets split because of `df["b"] = 100`
+    # which introduces additional refs, even when those of `view` go out of scopes
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 100
+    if using_copy_on_write:
+        # Setitem split the block. Since the old block shared data with view
+        # all the new blocks are referencing view and each other. When view
+        # goes out of scope, they don't share data with any other block,
+        # so we should not trigger a copy
+        mark = pytest.mark.xfail(
+            reason="blk.delete does not track references correctly"
+        )
+        request.applymarker(mark)
+        assert np.shares_memory(arr, get_array(df, "a"))
+
+
+def test_out_of_scope(using_copy_on_write):
+    def func():
+        df = DataFrame({"a": [1, 2], "b": 1.5, "c": 1})
+        # create some subset
+        result = df[["a", "b"]]
+        return result
+
+    result = func()
+    if using_copy_on_write:
+        assert not result._mgr.blocks[0].refs.has_reference()
+        assert not result._mgr.blocks[1].refs.has_reference()
+
+
+def test_delete(using_copy_on_write):
+    df = DataFrame(
+        np.random.default_rng(2).standard_normal((4, 3)), columns=["a", "b", "c"]
+    )
+    del df["b"]
+    if using_copy_on_write:
+        assert not df._mgr.blocks[0].refs.has_reference()
+        assert not df._mgr.blocks[1].refs.has_reference()
+
+    df = df[["a"]]
+    if using_copy_on_write:
+        assert not df._mgr.blocks[0].refs.has_reference()
+
+
+def test_delete_reference(using_copy_on_write):
+    df = DataFrame(
+        np.random.default_rng(2).standard_normal((4, 3)), columns=["a", "b", "c"]
+    )
+    x = df[:]
+    del df["b"]
+    if using_copy_on_write:
+        assert df._mgr.blocks[0].refs.has_reference()
+        assert df._mgr.blocks[1].refs.has_reference()
+        assert x._mgr.blocks[0].refs.has_reference()

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_functions.py

@@ -0,0 +1,396 @@
+import numpy as np
+import pytest
+
+from pandas import (
+    DataFrame,
+    Index,
+    Series,
+    concat,
+    merge,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+def test_concat_frames(using_copy_on_write):
+    df = DataFrame({"b": ["a"] * 3})
+    df2 = DataFrame({"a": ["a"] * 3})
+    df_orig = df.copy()
+    result = concat([df, df2], axis=1)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "b"), get_array(df, "b"))
+        assert np.shares_memory(get_array(result, "a"), get_array(df2, "a"))
+    else:
+        assert not np.shares_memory(get_array(result, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(result, "a"), get_array(df2, "a"))
+
+    result.iloc[0, 0] = "d"
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "b"), get_array(df, "b"))
+        assert np.shares_memory(get_array(result, "a"), get_array(df2, "a"))
+
+    result.iloc[0, 1] = "d"
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df2, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_concat_frames_updating_input(using_copy_on_write):
+    df = DataFrame({"b": ["a"] * 3})
+    df2 = DataFrame({"a": ["a"] * 3})
+    result = concat([df, df2], axis=1)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "b"), get_array(df, "b"))
+        assert np.shares_memory(get_array(result, "a"), get_array(df2, "a"))
+    else:
+        assert not np.shares_memory(get_array(result, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(result, "a"), get_array(df2, "a"))
+
+    expected = result.copy()
+    df.iloc[0, 0] = "d"
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "b"), get_array(df, "b"))
+        assert np.shares_memory(get_array(result, "a"), get_array(df2, "a"))
+
+    df2.iloc[0, 0] = "d"
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df2, "a"))
+    tm.assert_frame_equal(result, expected)
+
+
+def test_concat_series(using_copy_on_write):
+    ser = Series([1, 2], name="a")
+    ser2 = Series([3, 4], name="b")
+    ser_orig = ser.copy()
+    ser2_orig = ser2.copy()
+    result = concat([ser, ser2], axis=1)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), ser.values)
+        assert np.shares_memory(get_array(result, "b"), ser2.values)
+    else:
+        assert not np.shares_memory(get_array(result, "a"), ser.values)
+        assert not np.shares_memory(get_array(result, "b"), ser2.values)
+
+    result.iloc[0, 0] = 100
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), ser.values)
+        assert np.shares_memory(get_array(result, "b"), ser2.values)
+
+    result.iloc[0, 1] = 1000
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "b"), ser2.values)
+    tm.assert_series_equal(ser, ser_orig)
+    tm.assert_series_equal(ser2, ser2_orig)
+
+
+def test_concat_frames_chained(using_copy_on_write):
+    df1 = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]})
+    df2 = DataFrame({"c": [4, 5, 6]})
+    df3 = DataFrame({"d": [4, 5, 6]})
+    result = concat([concat([df1, df2], axis=1), df3], axis=1)
+    expected = result.copy()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "c"), get_array(df2, "c"))
+        assert np.shares_memory(get_array(result, "d"), get_array(df3, "d"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert not np.shares_memory(get_array(result, "c"), get_array(df2, "c"))
+        assert not np.shares_memory(get_array(result, "d"), get_array(df3, "d"))
+
+    df1.iloc[0, 0] = 100
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+
+    tm.assert_frame_equal(result, expected)
+
+
+def test_concat_series_chained(using_copy_on_write):
+    ser1 = Series([1, 2, 3], name="a")
+    ser2 = Series([4, 5, 6], name="c")
+    ser3 = Series([4, 5, 6], name="d")
+    result = concat([concat([ser1, ser2], axis=1), ser3], axis=1)
+    expected = result.copy()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(ser1, "a"))
+        assert np.shares_memory(get_array(result, "c"), get_array(ser2, "c"))
+        assert np.shares_memory(get_array(result, "d"), get_array(ser3, "d"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(ser1, "a"))
+        assert not np.shares_memory(get_array(result, "c"), get_array(ser2, "c"))
+        assert not np.shares_memory(get_array(result, "d"), get_array(ser3, "d"))
+
+    ser1.iloc[0] = 100
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(ser1, "a"))
+
+    tm.assert_frame_equal(result, expected)
+
+
+def test_concat_series_updating_input(using_copy_on_write):
+    ser = Series([1, 2], name="a")
+    ser2 = Series([3, 4], name="b")
+    expected = DataFrame({"a": [1, 2], "b": [3, 4]})
+    result = concat([ser, ser2], axis=1)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(ser, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(ser2, "b"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(ser, "a"))
+        assert not np.shares_memory(get_array(result, "b"), get_array(ser2, "b"))
+
+    ser.iloc[0] = 100
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(ser, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(ser2, "b"))
+    tm.assert_frame_equal(result, expected)
+
+    ser2.iloc[0] = 1000
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "b"), get_array(ser2, "b"))
+    tm.assert_frame_equal(result, expected)
+
+
+def test_concat_mixed_series_frame(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "c": 1})
+    ser = Series([4, 5, 6], name="d")
+    result = concat([df, ser], axis=1)
+    expected = result.copy()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+        assert np.shares_memory(get_array(result, "c"), get_array(df, "c"))
+        assert np.shares_memory(get_array(result, "d"), get_array(ser, "d"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+        assert not np.shares_memory(get_array(result, "c"), get_array(df, "c"))
+        assert not np.shares_memory(get_array(result, "d"), get_array(ser, "d"))
+
+    ser.iloc[0] = 100
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "d"), get_array(ser, "d"))
+
+    df.iloc[0, 0] = 100
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(result, expected)
+
+
+@pytest.mark.parametrize("copy", [True, None, False])
+def test_concat_copy_keyword(using_copy_on_write, copy):
+    df = DataFrame({"a": [1, 2]})
+    df2 = DataFrame({"b": [1.5, 2.5]})
+
+    result = concat([df, df2], axis=1, copy=copy)
+
+    if using_copy_on_write or copy is False:
+        assert np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+        assert np.shares_memory(get_array(df2, "b"), get_array(result, "b"))
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(result, "b"))
+
+
+@pytest.mark.parametrize(
+    "func",
+    [
+        lambda df1, df2, **kwargs: df1.merge(df2, **kwargs),
+        lambda df1, df2, **kwargs: merge(df1, df2, **kwargs),
+    ],
+)
+def test_merge_on_key(using_copy_on_write, func):
+    df1 = DataFrame({"key": ["a", "b", "c"], "a": [1, 2, 3]})
+    df2 = DataFrame({"key": ["a", "b", "c"], "b": [4, 5, 6]})
+    df1_orig = df1.copy()
+    df2_orig = df2.copy()
+
+    result = func(df1, df2, on="key")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+        assert np.shares_memory(get_array(result, "key"), get_array(df1, "key"))
+        assert not np.shares_memory(get_array(result, "key"), get_array(df2, "key"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert not np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+
+    result.iloc[0, 1] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+
+    result.iloc[0, 2] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+    tm.assert_frame_equal(df1, df1_orig)
+    tm.assert_frame_equal(df2, df2_orig)
+
+
+def test_merge_on_index(using_copy_on_write):
+    df1 = DataFrame({"a": [1, 2, 3]})
+    df2 = DataFrame({"b": [4, 5, 6]})
+    df1_orig = df1.copy()
+    df2_orig = df2.copy()
+
+    result = merge(df1, df2, left_index=True, right_index=True)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert not np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+
+    result.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+
+    result.iloc[0, 1] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+    tm.assert_frame_equal(df1, df1_orig)
+    tm.assert_frame_equal(df2, df2_orig)
+
+
+@pytest.mark.parametrize(
+    "func, how",
+    [
+        (lambda df1, df2, **kwargs: merge(df2, df1, on="key", **kwargs), "right"),
+        (lambda df1, df2, **kwargs: merge(df1, df2, on="key", **kwargs), "left"),
+    ],
+)
+def test_merge_on_key_enlarging_one(using_copy_on_write, func, how):
+    df1 = DataFrame({"key": ["a", "b", "c"], "a": [1, 2, 3]})
+    df2 = DataFrame({"key": ["a", "b"], "b": [4, 5]})
+    df1_orig = df1.copy()
+    df2_orig = df2.copy()
+
+    result = func(df1, df2, how=how)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert not np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+        assert df2._mgr._has_no_reference(1)
+        assert df2._mgr._has_no_reference(0)
+        assert np.shares_memory(get_array(result, "key"), get_array(df1, "key")) is (
+            how == "left"
+        )
+        assert not np.shares_memory(get_array(result, "key"), get_array(df2, "key"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert not np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+
+    if how == "left":
+        result.iloc[0, 1] = 0
+    else:
+        result.iloc[0, 2] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+    tm.assert_frame_equal(df1, df1_orig)
+    tm.assert_frame_equal(df2, df2_orig)
+
+
+@pytest.mark.parametrize("copy", [True, None, False])
+def test_merge_copy_keyword(using_copy_on_write, copy):
+    df = DataFrame({"a": [1, 2]})
+    df2 = DataFrame({"b": [3, 4.5]})
+
+    result = df.merge(df2, copy=copy, left_index=True, right_index=True)
+
+    if using_copy_on_write or copy is False:
+        assert np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+        assert np.shares_memory(get_array(df2, "b"), get_array(result, "b"))
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(result, "b"))
+
+
+def test_join_on_key(using_copy_on_write):
+    df_index = Index(["a", "b", "c"], name="key")
+
+    df1 = DataFrame({"a": [1, 2, 3]}, index=df_index.copy(deep=True))
+    df2 = DataFrame({"b": [4, 5, 6]}, index=df_index.copy(deep=True))
+
+    df1_orig = df1.copy()
+    df2_orig = df2.copy()
+
+    result = df1.join(df2, on="key")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+        assert np.shares_memory(get_array(result.index), get_array(df1.index))
+        assert not np.shares_memory(get_array(result.index), get_array(df2.index))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert not np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+
+    result.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+
+    result.iloc[0, 1] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "b"), get_array(df2, "b"))
+
+    tm.assert_frame_equal(df1, df1_orig)
+    tm.assert_frame_equal(df2, df2_orig)
+
+
+def test_join_multiple_dataframes_on_key(using_copy_on_write):
+    df_index = Index(["a", "b", "c"], name="key")
+
+    df1 = DataFrame({"a": [1, 2, 3]}, index=df_index.copy(deep=True))
+    dfs_list = [
+        DataFrame({"b": [4, 5, 6]}, index=df_index.copy(deep=True)),
+        DataFrame({"c": [7, 8, 9]}, index=df_index.copy(deep=True)),
+    ]
+
+    df1_orig = df1.copy()
+    dfs_list_orig = [df.copy() for df in dfs_list]
+
+    result = df1.join(dfs_list)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(dfs_list[0], "b"))
+        assert np.shares_memory(get_array(result, "c"), get_array(dfs_list[1], "c"))
+        assert np.shares_memory(get_array(result.index), get_array(df1.index))
+        assert not np.shares_memory(
+            get_array(result.index), get_array(dfs_list[0].index)
+        )
+        assert not np.shares_memory(
+            get_array(result.index), get_array(dfs_list[1].index)
+        )
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert not np.shares_memory(get_array(result, "b"), get_array(dfs_list[0], "b"))
+        assert not np.shares_memory(get_array(result, "c"), get_array(dfs_list[1], "c"))
+
+    result.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
+        assert np.shares_memory(get_array(result, "b"), get_array(dfs_list[0], "b"))
+        assert np.shares_memory(get_array(result, "c"), get_array(dfs_list[1], "c"))
+
+    result.iloc[0, 1] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "b"), get_array(dfs_list[0], "b"))
+        assert np.shares_memory(get_array(result, "c"), get_array(dfs_list[1], "c"))
+
+    result.iloc[0, 2] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "c"), get_array(dfs_list[1], "c"))
+
+    tm.assert_frame_equal(df1, df1_orig)
+    for df, df_orig in zip(dfs_list, dfs_list_orig):
+        tm.assert_frame_equal(df, df_orig)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_indexing.py

@@ -0,0 +1,1266 @@
+import numpy as np
+import pytest
+
+from pandas.errors import SettingWithCopyWarning
+
+from pandas.core.dtypes.common import is_float_dtype
+
+import pandas as pd
+from pandas import (
+    DataFrame,
+    Series,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+@pytest.fixture(params=["numpy", "nullable"])
+def backend(request):
+    if request.param == "numpy":
+
+        def make_dataframe(*args, **kwargs):
+            return DataFrame(*args, **kwargs)
+
+        def make_series(*args, **kwargs):
+            return Series(*args, **kwargs)
+
+    elif request.param == "nullable":
+
+        def make_dataframe(*args, **kwargs):
+            df = DataFrame(*args, **kwargs)
+            df_nullable = df.convert_dtypes()
+            # convert_dtypes will try to cast float to int if there is no loss in
+            # precision -> undo that change
+            for col in df.columns:
+                if is_float_dtype(df[col].dtype) and not is_float_dtype(
+                    df_nullable[col].dtype
+                ):
+                    df_nullable[col] = df_nullable[col].astype("Float64")
+            # copy final result to ensure we start with a fully self-owning DataFrame
+            return df_nullable.copy()
+
+        def make_series(*args, **kwargs):
+            ser = Series(*args, **kwargs)
+            return ser.convert_dtypes().copy()
+
+    return request.param, make_dataframe, make_series
+
+
+# -----------------------------------------------------------------------------
+# Indexing operations taking subset + modifying the subset/parent
+
+
+def test_subset_column_selection(backend, using_copy_on_write):
+    # Case: taking a subset of the columns of a DataFrame
+    # + afterwards modifying the subset
+    _, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+
+    subset = df[["a", "c"]]
+
+    if using_copy_on_write:
+        # the subset shares memory ...
+        assert np.shares_memory(get_array(subset, "a"), get_array(df, "a"))
+        # ... but uses CoW when being modified
+        subset.iloc[0, 0] = 0
+    else:
+        assert not np.shares_memory(get_array(subset, "a"), get_array(df, "a"))
+        # INFO this no longer raise warning since pandas 1.4
+        # with pd.option_context("chained_assignment", "warn"):
+        #     with tm.assert_produces_warning(SettingWithCopyWarning):
+        subset.iloc[0, 0] = 0
+
+    assert not np.shares_memory(get_array(subset, "a"), get_array(df, "a"))
+
+    expected = DataFrame({"a": [0, 2, 3], "c": [0.1, 0.2, 0.3]})
+    tm.assert_frame_equal(subset, expected)
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_subset_column_selection_modify_parent(backend, using_copy_on_write):
+    # Case: taking a subset of the columns of a DataFrame
+    # + afterwards modifying the parent
+    _, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+
+    subset = df[["a", "c"]]
+
+    if using_copy_on_write:
+        # the subset shares memory ...
+        assert np.shares_memory(get_array(subset, "a"), get_array(df, "a"))
+        # ... but parent uses CoW parent when it is modified
+    df.iloc[0, 0] = 0
+
+    assert not np.shares_memory(get_array(subset, "a"), get_array(df, "a"))
+    if using_copy_on_write:
+        # different column/block still shares memory
+        assert np.shares_memory(get_array(subset, "c"), get_array(df, "c"))
+
+    expected = DataFrame({"a": [1, 2, 3], "c": [0.1, 0.2, 0.3]})
+    tm.assert_frame_equal(subset, expected)
+
+
+def test_subset_row_slice(backend, using_copy_on_write, warn_copy_on_write):
+    # Case: taking a subset of the rows of a DataFrame using a slice
+    # + afterwards modifying the subset
+    _, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+
+    subset = df[1:3]
+    subset._mgr._verify_integrity()
+
+    assert np.shares_memory(get_array(subset, "a"), get_array(df, "a"))
+
+    if using_copy_on_write:
+        subset.iloc[0, 0] = 0
+        assert not np.shares_memory(get_array(subset, "a"), get_array(df, "a"))
+
+    else:
+        # INFO this no longer raise warning since pandas 1.4
+        # with pd.option_context("chained_assignment", "warn"):
+        #     with tm.assert_produces_warning(SettingWithCopyWarning):
+        with tm.assert_cow_warning(warn_copy_on_write):
+            subset.iloc[0, 0] = 0
+
+    subset._mgr._verify_integrity()
+
+    expected = DataFrame({"a": [0, 3], "b": [5, 6], "c": [0.2, 0.3]}, index=range(1, 3))
+    tm.assert_frame_equal(subset, expected)
+    if using_copy_on_write:
+        # original parent dataframe is not modified (CoW)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        # original parent dataframe is actually updated
+        df_orig.iloc[1, 0] = 0
+        tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+def test_subset_column_slice(
+    backend, using_copy_on_write, warn_copy_on_write, using_array_manager, dtype
+):
+    # Case: taking a subset of the columns of a DataFrame using a slice
+    # + afterwards modifying the subset
+    dtype_backend, DataFrame, _ = backend
+    single_block = (
+        dtype == "int64" and dtype_backend == "numpy"
+    ) and not using_array_manager
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}
+    )
+    df_orig = df.copy()
+
+    subset = df.iloc[:, 1:]
+    subset._mgr._verify_integrity()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(subset, "b"), get_array(df, "b"))
+
+        subset.iloc[0, 0] = 0
+        assert not np.shares_memory(get_array(subset, "b"), get_array(df, "b"))
+    elif warn_copy_on_write:
+        with tm.assert_cow_warning(single_block):
+            subset.iloc[0, 0] = 0
+    else:
+        # we only get a warning in case of a single block
+        warn = SettingWithCopyWarning if single_block else None
+        with pd.option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(warn):
+                subset.iloc[0, 0] = 0
+
+    expected = DataFrame({"b": [0, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)})
+    tm.assert_frame_equal(subset, expected)
+    # original parent dataframe is not modified (also not for BlockManager case,
+    # except for single block)
+    if not using_copy_on_write and (using_array_manager or single_block):
+        df_orig.iloc[0, 1] = 0
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+@pytest.mark.parametrize(
+    "row_indexer",
+    [slice(1, 2), np.array([False, True, True]), np.array([1, 2])],
+    ids=["slice", "mask", "array"],
+)
+@pytest.mark.parametrize(
+    "column_indexer",
+    [slice("b", "c"), np.array([False, True, True]), ["b", "c"]],
+    ids=["slice", "mask", "array"],
+)
+def test_subset_loc_rows_columns(
+    backend,
+    dtype,
+    row_indexer,
+    column_indexer,
+    using_array_manager,
+    using_copy_on_write,
+    warn_copy_on_write,
+):
+    # Case: taking a subset of the rows+columns of a DataFrame using .loc
+    # + afterwards modifying the subset
+    # Generic test for several combinations of row/column indexers, not all
+    # of those could actually return a view / need CoW (so this test is not
+    # checking memory sharing, only ensuring subsequent mutation doesn't
+    # affect the parent dataframe)
+    dtype_backend, DataFrame, _ = backend
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}
+    )
+    df_orig = df.copy()
+
+    subset = df.loc[row_indexer, column_indexer]
+
+    # a few corner cases _do_ actually modify the parent (with both row and column
+    # slice, and in case of ArrayManager or BlockManager with single block)
+    mutate_parent = (
+        isinstance(row_indexer, slice)
+        and isinstance(column_indexer, slice)
+        and (
+            using_array_manager
+            or (
+                dtype == "int64"
+                and dtype_backend == "numpy"
+                and not using_copy_on_write
+            )
+        )
+    )
+
+    # modifying the subset never modifies the parent
+    with tm.assert_cow_warning(warn_copy_on_write and mutate_parent):
+        subset.iloc[0, 0] = 0
+
+    expected = DataFrame(
+        {"b": [0, 6], "c": np.array([8, 9], dtype=dtype)}, index=range(1, 3)
+    )
+    tm.assert_frame_equal(subset, expected)
+    if mutate_parent:
+        df_orig.iloc[1, 1] = 0
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+@pytest.mark.parametrize(
+    "row_indexer",
+    [slice(1, 3), np.array([False, True, True]), np.array([1, 2])],
+    ids=["slice", "mask", "array"],
+)
+@pytest.mark.parametrize(
+    "column_indexer",
+    [slice(1, 3), np.array([False, True, True]), [1, 2]],
+    ids=["slice", "mask", "array"],
+)
+def test_subset_iloc_rows_columns(
+    backend,
+    dtype,
+    row_indexer,
+    column_indexer,
+    using_array_manager,
+    using_copy_on_write,
+    warn_copy_on_write,
+):
+    # Case: taking a subset of the rows+columns of a DataFrame using .iloc
+    # + afterwards modifying the subset
+    # Generic test for several combinations of row/column indexers, not all
+    # of those could actually return a view / need CoW (so this test is not
+    # checking memory sharing, only ensuring subsequent mutation doesn't
+    # affect the parent dataframe)
+    dtype_backend, DataFrame, _ = backend
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}
+    )
+    df_orig = df.copy()
+
+    subset = df.iloc[row_indexer, column_indexer]
+
+    # a few corner cases _do_ actually modify the parent (with both row and column
+    # slice, and in case of ArrayManager or BlockManager with single block)
+    mutate_parent = (
+        isinstance(row_indexer, slice)
+        and isinstance(column_indexer, slice)
+        and (
+            using_array_manager
+            or (
+                dtype == "int64"
+                and dtype_backend == "numpy"
+                and not using_copy_on_write
+            )
+        )
+    )
+
+    # modifying the subset never modifies the parent
+    with tm.assert_cow_warning(warn_copy_on_write and mutate_parent):
+        subset.iloc[0, 0] = 0
+
+    expected = DataFrame(
+        {"b": [0, 6], "c": np.array([8, 9], dtype=dtype)}, index=range(1, 3)
+    )
+    tm.assert_frame_equal(subset, expected)
+    if mutate_parent:
+        df_orig.iloc[1, 1] = 0
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "indexer",
+    [slice(0, 2), np.array([True, True, False]), np.array([0, 1])],
+    ids=["slice", "mask", "array"],
+)
+def test_subset_set_with_row_indexer(
+    backend, indexer_si, indexer, using_copy_on_write, warn_copy_on_write
+):
+    # Case: setting values with a row indexer on a viewing subset
+    # subset[indexer] = value and subset.iloc[indexer] = value
+    _, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3, 4], "b": [4, 5, 6, 7], "c": [0.1, 0.2, 0.3, 0.4]})
+    df_orig = df.copy()
+    subset = df[1:4]
+
+    if (
+        indexer_si is tm.setitem
+        and isinstance(indexer, np.ndarray)
+        and indexer.dtype == "int"
+    ):
+        pytest.skip("setitem with labels selects on columns")
+
+    if using_copy_on_write:
+        indexer_si(subset)[indexer] = 0
+    elif warn_copy_on_write:
+        with tm.assert_cow_warning():
+            indexer_si(subset)[indexer] = 0
+    else:
+        # INFO iloc no longer raises warning since pandas 1.4
+        warn = SettingWithCopyWarning if indexer_si is tm.setitem else None
+        with pd.option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(warn):
+                indexer_si(subset)[indexer] = 0
+
+    expected = DataFrame(
+        {"a": [0, 0, 4], "b": [0, 0, 7], "c": [0.0, 0.0, 0.4]}, index=range(1, 4)
+    )
+    tm.assert_frame_equal(subset, expected)
+    if using_copy_on_write:
+        # original parent dataframe is not modified (CoW)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        # original parent dataframe is actually updated
+        df_orig[1:3] = 0
+        tm.assert_frame_equal(df, df_orig)
+
+
+def test_subset_set_with_mask(backend, using_copy_on_write, warn_copy_on_write):
+    # Case: setting values with a mask on a viewing subset: subset[mask] = value
+    _, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3, 4], "b": [4, 5, 6, 7], "c": [0.1, 0.2, 0.3, 0.4]})
+    df_orig = df.copy()
+    subset = df[1:4]
+
+    mask = subset > 3
+
+    if using_copy_on_write:
+        subset[mask] = 0
+    elif warn_copy_on_write:
+        with tm.assert_cow_warning():
+            subset[mask] = 0
+    else:
+        with pd.option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(SettingWithCopyWarning):
+                subset[mask] = 0
+
+    expected = DataFrame(
+        {"a": [2, 3, 0], "b": [0, 0, 0], "c": [0.20, 0.3, 0.4]}, index=range(1, 4)
+    )
+    tm.assert_frame_equal(subset, expected)
+    if using_copy_on_write:
+        # original parent dataframe is not modified (CoW)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        # original parent dataframe is actually updated
+        df_orig.loc[3, "a"] = 0
+        df_orig.loc[1:3, "b"] = 0
+        tm.assert_frame_equal(df, df_orig)
+
+
+def test_subset_set_column(backend, using_copy_on_write, warn_copy_on_write):
+    # Case: setting a single column on a viewing subset -> subset[col] = value
+    dtype_backend, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    subset = df[1:3]
+
+    if dtype_backend == "numpy":
+        arr = np.array([10, 11], dtype="int64")
+    else:
+        arr = pd.array([10, 11], dtype="Int64")
+
+    if using_copy_on_write or warn_copy_on_write:
+        subset["a"] = arr
+    else:
+        with pd.option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(SettingWithCopyWarning):
+                subset["a"] = arr
+
+    subset._mgr._verify_integrity()
+    expected = DataFrame(
+        {"a": [10, 11], "b": [5, 6], "c": [0.2, 0.3]}, index=range(1, 3)
+    )
+    tm.assert_frame_equal(subset, expected)
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+def test_subset_set_column_with_loc(
+    backend, using_copy_on_write, warn_copy_on_write, using_array_manager, dtype
+):
+    # Case: setting a single column with loc on a viewing subset
+    # -> subset.loc[:, col] = value
+    _, DataFrame, _ = backend
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}
+    )
+    df_orig = df.copy()
+    subset = df[1:3]
+
+    if using_copy_on_write:
+        subset.loc[:, "a"] = np.array([10, 11], dtype="int64")
+    elif warn_copy_on_write:
+        with tm.assert_cow_warning():
+            subset.loc[:, "a"] = np.array([10, 11], dtype="int64")
+    else:
+        with pd.option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(
+                None,
+                raise_on_extra_warnings=not using_array_manager,
+            ):
+                subset.loc[:, "a"] = np.array([10, 11], dtype="int64")
+
+    subset._mgr._verify_integrity()
+    expected = DataFrame(
+        {"a": [10, 11], "b": [5, 6], "c": np.array([8, 9], dtype=dtype)},
+        index=range(1, 3),
+    )
+    tm.assert_frame_equal(subset, expected)
+    if using_copy_on_write:
+        # original parent dataframe is not modified (CoW)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        # original parent dataframe is actually updated
+        df_orig.loc[1:3, "a"] = np.array([10, 11], dtype="int64")
+        tm.assert_frame_equal(df, df_orig)
+
+
+def test_subset_set_column_with_loc2(
+    backend, using_copy_on_write, warn_copy_on_write, using_array_manager
+):
+    # Case: setting a single column with loc on a viewing subset
+    # -> subset.loc[:, col] = value
+    # separate test for case of DataFrame of a single column -> takes a separate
+    # code path
+    _, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3]})
+    df_orig = df.copy()
+    subset = df[1:3]
+
+    if using_copy_on_write:
+        subset.loc[:, "a"] = 0
+    elif warn_copy_on_write:
+        with tm.assert_cow_warning():
+            subset.loc[:, "a"] = 0
+    else:
+        with pd.option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(
+                None,
+                raise_on_extra_warnings=not using_array_manager,
+            ):
+                subset.loc[:, "a"] = 0
+
+    subset._mgr._verify_integrity()
+    expected = DataFrame({"a": [0, 0]}, index=range(1, 3))
+    tm.assert_frame_equal(subset, expected)
+    if using_copy_on_write:
+        # original parent dataframe is not modified (CoW)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        # original parent dataframe is actually updated
+        df_orig.loc[1:3, "a"] = 0
+        tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+def test_subset_set_columns(backend, using_copy_on_write, warn_copy_on_write, dtype):
+    # Case: setting multiple columns on a viewing subset
+    # -> subset[[col1, col2]] = value
+    dtype_backend, DataFrame, _ = backend
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}
+    )
+    df_orig = df.copy()
+    subset = df[1:3]
+
+    if using_copy_on_write or warn_copy_on_write:
+        subset[["a", "c"]] = 0
+    else:
+        with pd.option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(SettingWithCopyWarning):
+                subset[["a", "c"]] = 0
+
+    subset._mgr._verify_integrity()
+    if using_copy_on_write:
+        # first and third column should certainly have no references anymore
+        assert all(subset._mgr._has_no_reference(i) for i in [0, 2])
+    expected = DataFrame({"a": [0, 0], "b": [5, 6], "c": [0, 0]}, index=range(1, 3))
+    if dtype_backend == "nullable":
+        # there is not yet a global option, so overriding a column by setting a scalar
+        # defaults to numpy dtype even if original column was nullable
+        expected["a"] = expected["a"].astype("int64")
+        expected["c"] = expected["c"].astype("int64")
+
+    tm.assert_frame_equal(subset, expected)
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "indexer",
+    [slice("a", "b"), np.array([True, True, False]), ["a", "b"]],
+    ids=["slice", "mask", "array"],
+)
+def test_subset_set_with_column_indexer(
+    backend, indexer, using_copy_on_write, warn_copy_on_write
+):
+    # Case: setting multiple columns with a column indexer on a viewing subset
+    # -> subset.loc[:, [col1, col2]] = value
+    _, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3], "c": [4, 5, 6]})
+    df_orig = df.copy()
+    subset = df[1:3]
+
+    if using_copy_on_write:
+        subset.loc[:, indexer] = 0
+    elif warn_copy_on_write:
+        with tm.assert_cow_warning():
+            subset.loc[:, indexer] = 0
+    else:
+        with pd.option_context("chained_assignment", "warn"):
+            # As of 2.0, this setitem attempts (successfully) to set values
+            #  inplace, so the assignment is not chained.
+            subset.loc[:, indexer] = 0
+
+    subset._mgr._verify_integrity()
+    expected = DataFrame({"a": [0, 0], "b": [0.0, 0.0], "c": [5, 6]}, index=range(1, 3))
+    tm.assert_frame_equal(subset, expected)
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        # pre-2.0, in the mixed case with BlockManager, only column "a"
+        #  would be mutated in the parent frame. this changed with the
+        #  enforcement of GH#45333
+        df_orig.loc[1:2, ["a", "b"]] = 0
+        tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda df: df[["a", "b"]][0:2],
+        lambda df: df[0:2][["a", "b"]],
+        lambda df: df[["a", "b"]].iloc[0:2],
+        lambda df: df[["a", "b"]].loc[0:1],
+        lambda df: df[0:2].iloc[:, 0:2],
+        lambda df: df[0:2].loc[:, "a":"b"],  # type: ignore[misc]
+    ],
+    ids=[
+        "row-getitem-slice",
+        "column-getitem",
+        "row-iloc-slice",
+        "row-loc-slice",
+        "column-iloc-slice",
+        "column-loc-slice",
+    ],
+)
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+def test_subset_chained_getitem(
+    request,
+    backend,
+    method,
+    dtype,
+    using_copy_on_write,
+    using_array_manager,
+    warn_copy_on_write,
+):
+    # Case: creating a subset using multiple, chained getitem calls using views
+    # still needs to guarantee proper CoW behaviour
+    _, DataFrame, _ = backend
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}
+    )
+    df_orig = df.copy()
+
+    # when not using CoW, it depends on whether we have a single block or not
+    # and whether we are slicing the columns -> in that case we have a view
+    test_callspec = request.node.callspec.id
+    if not using_array_manager:
+        subset_is_view = test_callspec in (
+            "numpy-single-block-column-iloc-slice",
+            "numpy-single-block-column-loc-slice",
+        )
+    else:
+        # with ArrayManager, it doesn't matter whether we have
+        # single vs mixed block or numpy vs nullable dtypes
+        subset_is_view = test_callspec.endswith(
+            ("column-iloc-slice", "column-loc-slice")
+        )
+
+    # modify subset -> don't modify parent
+    subset = method(df)
+
+    with tm.assert_cow_warning(warn_copy_on_write and subset_is_view):
+        subset.iloc[0, 0] = 0
+    if using_copy_on_write or (not subset_is_view):
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert df.iloc[0, 0] == 0
+
+    # modify parent -> don't modify subset
+    subset = method(df)
+    with tm.assert_cow_warning(warn_copy_on_write and subset_is_view):
+        df.iloc[0, 0] = 0
+    expected = DataFrame({"a": [1, 2], "b": [4, 5]})
+    if using_copy_on_write or not subset_is_view:
+        tm.assert_frame_equal(subset, expected)
+    else:
+        assert subset.iloc[0, 0] == 0
+
+
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+def test_subset_chained_getitem_column(
+    backend, dtype, using_copy_on_write, warn_copy_on_write
+):
+    # Case: creating a subset using multiple, chained getitem calls using views
+    # still needs to guarantee proper CoW behaviour
+    dtype_backend, DataFrame, Series = backend
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}
+    )
+    df_orig = df.copy()
+
+    # modify subset -> don't modify parent
+    subset = df[:]["a"][0:2]
+    df._clear_item_cache()
+    with tm.assert_cow_warning(warn_copy_on_write):
+        subset.iloc[0] = 0
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert df.iloc[0, 0] == 0
+
+    # modify parent -> don't modify subset
+    subset = df[:]["a"][0:2]
+    df._clear_item_cache()
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 0
+    expected = Series([1, 2], name="a")
+    if using_copy_on_write:
+        tm.assert_series_equal(subset, expected)
+    else:
+        assert subset.iloc[0] == 0
+
+
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda s: s["a":"c"]["a":"b"],  # type: ignore[misc]
+        lambda s: s.iloc[0:3].iloc[0:2],
+        lambda s: s.loc["a":"c"].loc["a":"b"],  # type: ignore[misc]
+        lambda s: s.loc["a":"c"]  # type: ignore[misc]
+        .iloc[0:3]
+        .iloc[0:2]
+        .loc["a":"b"]  # type: ignore[misc]
+        .iloc[0:1],
+    ],
+    ids=["getitem", "iloc", "loc", "long-chain"],
+)
+def test_subset_chained_getitem_series(
+    backend, method, using_copy_on_write, warn_copy_on_write
+):
+    # Case: creating a subset using multiple, chained getitem calls using views
+    # still needs to guarantee proper CoW behaviour
+    _, _, Series = backend
+    s = Series([1, 2, 3], index=["a", "b", "c"])
+    s_orig = s.copy()
+
+    # modify subset -> don't modify parent
+    subset = method(s)
+    with tm.assert_cow_warning(warn_copy_on_write):
+        subset.iloc[0] = 0
+    if using_copy_on_write:
+        tm.assert_series_equal(s, s_orig)
+    else:
+        assert s.iloc[0] == 0
+
+    # modify parent -> don't modify subset
+    subset = s.iloc[0:3].iloc[0:2]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        s.iloc[0] = 0
+    expected = Series([1, 2], index=["a", "b"])
+    if using_copy_on_write:
+        tm.assert_series_equal(subset, expected)
+    else:
+        assert subset.iloc[0] == 0
+
+
+def test_subset_chained_single_block_row(
+    using_copy_on_write, using_array_manager, warn_copy_on_write
+):
+    # not parametrizing this for dtype backend, since this explicitly tests single block
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]})
+    df_orig = df.copy()
+
+    # modify subset -> don't modify parent
+    subset = df[:].iloc[0].iloc[0:2]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        subset.iloc[0] = 0
+    if using_copy_on_write or using_array_manager:
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert df.iloc[0, 0] == 0
+
+    # modify parent -> don't modify subset
+    subset = df[:].iloc[0].iloc[0:2]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 0
+    expected = Series([1, 4], index=["a", "b"], name=0)
+    if using_copy_on_write or using_array_manager:
+        tm.assert_series_equal(subset, expected)
+    else:
+        assert subset.iloc[0] == 0
+
+
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda df: df[:],
+        lambda df: df.loc[:, :],
+        lambda df: df.loc[:],
+        lambda df: df.iloc[:, :],
+        lambda df: df.iloc[:],
+    ],
+    ids=["getitem", "loc", "loc-rows", "iloc", "iloc-rows"],
+)
+def test_null_slice(backend, method, using_copy_on_write, warn_copy_on_write):
+    # Case: also all variants of indexing with a null slice (:) should return
+    # new objects to ensure we correctly use CoW for the results
+    dtype_backend, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]})
+    df_orig = df.copy()
+
+    df2 = method(df)
+
+    # we always return new objects (shallow copy), regardless of CoW or not
+    assert df2 is not df
+
+    # and those trigger CoW when mutated
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert df.iloc[0, 0] == 0
+
+
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda s: s[:],
+        lambda s: s.loc[:],
+        lambda s: s.iloc[:],
+    ],
+    ids=["getitem", "loc", "iloc"],
+)
+def test_null_slice_series(backend, method, using_copy_on_write, warn_copy_on_write):
+    _, _, Series = backend
+    s = Series([1, 2, 3], index=["a", "b", "c"])
+    s_orig = s.copy()
+
+    s2 = method(s)
+
+    # we always return new objects, regardless of CoW or not
+    assert s2 is not s
+
+    # and those trigger CoW when mutated
+    with tm.assert_cow_warning(warn_copy_on_write):
+        s2.iloc[0] = 0
+    if using_copy_on_write:
+        tm.assert_series_equal(s, s_orig)
+    else:
+        assert s.iloc[0] == 0
+
+
+# TODO add more tests modifying the parent
+
+
+# -----------------------------------------------------------------------------
+# Series -- Indexing operations taking subset + modifying the subset/parent
+
+
+def test_series_getitem_slice(backend, using_copy_on_write, warn_copy_on_write):
+    # Case: taking a slice of a Series + afterwards modifying the subset
+    _, _, Series = backend
+    s = Series([1, 2, 3], index=["a", "b", "c"])
+    s_orig = s.copy()
+
+    subset = s[:]
+    assert np.shares_memory(get_array(subset), get_array(s))
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        subset.iloc[0] = 0
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(subset), get_array(s))
+
+    expected = Series([0, 2, 3], index=["a", "b", "c"])
+    tm.assert_series_equal(subset, expected)
+
+    if using_copy_on_write:
+        # original parent series is not modified (CoW)
+        tm.assert_series_equal(s, s_orig)
+    else:
+        # original parent series is actually updated
+        assert s.iloc[0] == 0
+
+
+def test_series_getitem_ellipsis(using_copy_on_write, warn_copy_on_write):
+    # Case: taking a view of a Series using Ellipsis + afterwards modifying the subset
+    s = Series([1, 2, 3])
+    s_orig = s.copy()
+
+    subset = s[...]
+    assert np.shares_memory(get_array(subset), get_array(s))
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        subset.iloc[0] = 0
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(subset), get_array(s))
+
+    expected = Series([0, 2, 3])
+    tm.assert_series_equal(subset, expected)
+
+    if using_copy_on_write:
+        # original parent series is not modified (CoW)
+        tm.assert_series_equal(s, s_orig)
+    else:
+        # original parent series is actually updated
+        assert s.iloc[0] == 0
+
+
+@pytest.mark.parametrize(
+    "indexer",
+    [slice(0, 2), np.array([True, True, False]), np.array([0, 1])],
+    ids=["slice", "mask", "array"],
+)
+def test_series_subset_set_with_indexer(
+    backend, indexer_si, indexer, using_copy_on_write, warn_copy_on_write
+):
+    # Case: setting values in a viewing Series with an indexer
+    _, _, Series = backend
+    s = Series([1, 2, 3], index=["a", "b", "c"])
+    s_orig = s.copy()
+    subset = s[:]
+
+    warn = None
+    msg = "Series.__setitem__ treating keys as positions is deprecated"
+    if (
+        indexer_si is tm.setitem
+        and isinstance(indexer, np.ndarray)
+        and indexer.dtype.kind == "i"
+    ):
+        warn = FutureWarning
+    if warn_copy_on_write:
+        with tm.assert_cow_warning(raise_on_extra_warnings=warn is not None):
+            indexer_si(subset)[indexer] = 0
+    else:
+        with tm.assert_produces_warning(warn, match=msg):
+            indexer_si(subset)[indexer] = 0
+    expected = Series([0, 0, 3], index=["a", "b", "c"])
+    tm.assert_series_equal(subset, expected)
+
+    if using_copy_on_write:
+        tm.assert_series_equal(s, s_orig)
+    else:
+        tm.assert_series_equal(s, expected)
+
+
+# -----------------------------------------------------------------------------
+# del operator
+
+
+def test_del_frame(backend, using_copy_on_write, warn_copy_on_write):
+    # Case: deleting a column with `del` on a viewing child dataframe should
+    # not modify parent + update the references
+    dtype_backend, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df[:]
+
+    assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    del df2["b"]
+
+    assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+    tm.assert_frame_equal(df, df_orig)
+    tm.assert_frame_equal(df2, df_orig[["a", "c"]])
+    df2._mgr._verify_integrity()
+
+    with tm.assert_cow_warning(warn_copy_on_write and dtype_backend == "numpy"):
+        df.loc[0, "b"] = 200
+    assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+    df_orig = df.copy()
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df2.loc[0, "a"] = 100
+    if using_copy_on_write:
+        # modifying child after deleting a column still doesn't update parent
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert df.loc[0, "a"] == 100
+
+
+def test_del_series(backend):
+    _, _, Series = backend
+    s = Series([1, 2, 3], index=["a", "b", "c"])
+    s_orig = s.copy()
+    s2 = s[:]
+
+    assert np.shares_memory(get_array(s), get_array(s2))
+
+    del s2["a"]
+
+    assert not np.shares_memory(get_array(s), get_array(s2))
+    tm.assert_series_equal(s, s_orig)
+    tm.assert_series_equal(s2, s_orig[["b", "c"]])
+
+    # modifying s2 doesn't need copy on write (due to `del`, s2 is backed by new array)
+    values = s2.values
+    s2.loc["b"] = 100
+    assert values[0] == 100
+
+
+# -----------------------------------------------------------------------------
+# Accessing column as Series
+
+
+def test_column_as_series(
+    backend, using_copy_on_write, warn_copy_on_write, using_array_manager
+):
+    # Case: selecting a single column now also uses Copy-on-Write
+    dtype_backend, DataFrame, Series = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+
+    s = df["a"]
+
+    assert np.shares_memory(get_array(s, "a"), get_array(df, "a"))
+
+    if using_copy_on_write or using_array_manager:
+        s[0] = 0
+    else:
+        if warn_copy_on_write:
+            with tm.assert_cow_warning():
+                s[0] = 0
+        else:
+            warn = SettingWithCopyWarning if dtype_backend == "numpy" else None
+            with pd.option_context("chained_assignment", "warn"):
+                with tm.assert_produces_warning(warn):
+                    s[0] = 0
+
+    expected = Series([0, 2, 3], name="a")
+    tm.assert_series_equal(s, expected)
+    if using_copy_on_write:
+        # assert not np.shares_memory(s.values, get_array(df, "a"))
+        tm.assert_frame_equal(df, df_orig)
+        # ensure cached series on getitem is not the changed series
+        tm.assert_series_equal(df["a"], df_orig["a"])
+    else:
+        df_orig.iloc[0, 0] = 0
+        tm.assert_frame_equal(df, df_orig)
+
+
+def test_column_as_series_set_with_upcast(
+    backend, using_copy_on_write, using_array_manager, warn_copy_on_write
+):
+    # Case: selecting a single column now also uses Copy-on-Write -> when
+    # setting a value causes an upcast, we don't need to update the parent
+    # DataFrame through the cache mechanism
+    dtype_backend, DataFrame, Series = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+
+    s = df["a"]
+    if dtype_backend == "nullable":
+        with tm.assert_cow_warning(warn_copy_on_write):
+            with pytest.raises(TypeError, match="Invalid value"):
+                s[0] = "foo"
+        expected = Series([1, 2, 3], name="a")
+    elif using_copy_on_write or warn_copy_on_write or using_array_manager:
+        # TODO(CoW-warn) assert the FutureWarning for CoW is also raised
+        with tm.assert_produces_warning(FutureWarning, match="incompatible dtype"):
+            s[0] = "foo"
+        expected = Series(["foo", 2, 3], dtype=object, name="a")
+    else:
+        with pd.option_context("chained_assignment", "warn"):
+            msg = "|".join(
+                [
+                    "A value is trying to be set on a copy of a slice from a DataFrame",
+                    "Setting an item of incompatible dtype is deprecated",
+                ]
+            )
+            with tm.assert_produces_warning(
+                (SettingWithCopyWarning, FutureWarning), match=msg
+            ):
+                s[0] = "foo"
+        expected = Series(["foo", 2, 3], dtype=object, name="a")
+
+    tm.assert_series_equal(s, expected)
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+        # ensure cached series on getitem is not the changed series
+        tm.assert_series_equal(df["a"], df_orig["a"])
+    else:
+        df_orig["a"] = expected
+        tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda df: df["a"],
+        lambda df: df.loc[:, "a"],
+        lambda df: df.iloc[:, 0],
+    ],
+    ids=["getitem", "loc", "iloc"],
+)
+def test_column_as_series_no_item_cache(
+    request,
+    backend,
+    method,
+    using_copy_on_write,
+    warn_copy_on_write,
+    using_array_manager,
+):
+    # Case: selecting a single column (which now also uses Copy-on-Write to protect
+    # the view) should always give a new object (i.e. not make use of a cache)
+    dtype_backend, DataFrame, _ = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+
+    s1 = method(df)
+    s2 = method(df)
+
+    is_iloc = "iloc" in request.node.name
+    if using_copy_on_write or warn_copy_on_write or is_iloc:
+        assert s1 is not s2
+    else:
+        assert s1 is s2
+
+    if using_copy_on_write or using_array_manager:
+        s1.iloc[0] = 0
+    elif warn_copy_on_write:
+        with tm.assert_cow_warning():
+            s1.iloc[0] = 0
+    else:
+        warn = SettingWithCopyWarning if dtype_backend == "numpy" else None
+        with pd.option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(warn):
+                s1.iloc[0] = 0
+
+    if using_copy_on_write:
+        tm.assert_series_equal(s2, df_orig["a"])
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert s2.iloc[0] == 0
+
+
+# TODO add tests for other indexing methods on the Series
+
+
+def test_dataframe_add_column_from_series(backend, using_copy_on_write):
+    # Case: adding a new column to a DataFrame from an existing column/series
+    # -> delays copy under CoW
+    _, DataFrame, Series = backend
+    df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]})
+
+    s = Series([10, 11, 12])
+    df["new"] = s
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "new"), get_array(s))
+    else:
+        assert not np.shares_memory(get_array(df, "new"), get_array(s))
+
+    # editing series -> doesn't modify column in frame
+    s[0] = 0
+    expected = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3], "new": [10, 11, 12]})
+    tm.assert_frame_equal(df, expected)
+
+
+@pytest.mark.parametrize("val", [100, "a"])
+@pytest.mark.parametrize(
+    "indexer_func, indexer",
+    [
+        (tm.loc, (0, "a")),
+        (tm.iloc, (0, 0)),
+        (tm.loc, ([0], "a")),
+        (tm.iloc, ([0], 0)),
+        (tm.loc, (slice(None), "a")),
+        (tm.iloc, (slice(None), 0)),
+    ],
+)
+@pytest.mark.parametrize(
+    "col", [[0.1, 0.2, 0.3], [7, 8, 9]], ids=["mixed-block", "single-block"]
+)
+def test_set_value_copy_only_necessary_column(
+    using_copy_on_write, warn_copy_on_write, indexer_func, indexer, val, col
+):
+    # When setting inplace, only copy column that is modified instead of the whole
+    # block (by splitting the block)
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": col})
+    df_orig = df.copy()
+    view = df[:]
+
+    if val == "a" and not warn_copy_on_write:
+        with tm.assert_produces_warning(
+            FutureWarning, match="Setting an item of incompatible dtype is deprecated"
+        ):
+            indexer_func(df)[indexer] = val
+    if val == "a" and warn_copy_on_write:
+        with tm.assert_produces_warning(
+            FutureWarning, match="incompatible dtype|Setting a value on a view"
+        ):
+            indexer_func(df)[indexer] = val
+    else:
+        with tm.assert_cow_warning(warn_copy_on_write and val == 100):
+            indexer_func(df)[indexer] = val
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "b"), get_array(view, "b"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(view, "a"))
+        tm.assert_frame_equal(view, df_orig)
+    else:
+        assert np.shares_memory(get_array(df, "c"), get_array(view, "c"))
+        if val == "a":
+            assert not np.shares_memory(get_array(df, "a"), get_array(view, "a"))
+        else:
+            assert np.shares_memory(get_array(df, "a"), get_array(view, "a"))
+
+
+def test_series_midx_slice(using_copy_on_write, warn_copy_on_write):
+    ser = Series([1, 2, 3], index=pd.MultiIndex.from_arrays([[1, 1, 2], [3, 4, 5]]))
+    ser_orig = ser.copy()
+    result = ser[1]
+    assert np.shares_memory(get_array(ser), get_array(result))
+    with tm.assert_cow_warning(warn_copy_on_write):
+        result.iloc[0] = 100
+    if using_copy_on_write:
+        tm.assert_series_equal(ser, ser_orig)
+    else:
+        expected = Series(
+            [100, 2, 3], index=pd.MultiIndex.from_arrays([[1, 1, 2], [3, 4, 5]])
+        )
+        tm.assert_series_equal(ser, expected)
+
+
+def test_getitem_midx_slice(
+    using_copy_on_write, warn_copy_on_write, using_array_manager
+):
+    df = DataFrame({("a", "x"): [1, 2], ("a", "y"): 1, ("b", "x"): 2})
+    df_orig = df.copy()
+    new_df = df[("a",)]
+
+    if using_copy_on_write:
+        assert not new_df._mgr._has_no_reference(0)
+
+    if not using_array_manager:
+        assert np.shares_memory(get_array(df, ("a", "x")), get_array(new_df, "x"))
+    if using_copy_on_write:
+        new_df.iloc[0, 0] = 100
+        tm.assert_frame_equal(df_orig, df)
+    else:
+        if warn_copy_on_write:
+            with tm.assert_cow_warning():
+                new_df.iloc[0, 0] = 100
+        else:
+            with pd.option_context("chained_assignment", "warn"):
+                with tm.assert_produces_warning(SettingWithCopyWarning):
+                    new_df.iloc[0, 0] = 100
+        assert df.iloc[0, 0] == 100
+
+
+def test_series_midx_tuples_slice(using_copy_on_write, warn_copy_on_write):
+    ser = Series(
+        [1, 2, 3],
+        index=pd.MultiIndex.from_tuples([((1, 2), 3), ((1, 2), 4), ((2, 3), 4)]),
+    )
+    result = ser[(1, 2)]
+    assert np.shares_memory(get_array(ser), get_array(result))
+    with tm.assert_cow_warning(warn_copy_on_write):
+        result.iloc[0] = 100
+    if using_copy_on_write:
+        expected = Series(
+            [1, 2, 3],
+            index=pd.MultiIndex.from_tuples([((1, 2), 3), ((1, 2), 4), ((2, 3), 4)]),
+        )
+        tm.assert_series_equal(ser, expected)
+
+
+def test_midx_read_only_bool_indexer():
+    # GH#56635
+    def mklbl(prefix, n):
+        return [f"{prefix}{i}" for i in range(n)]
+
+    idx = pd.MultiIndex.from_product(
+        [mklbl("A", 4), mklbl("B", 2), mklbl("C", 4), mklbl("D", 2)]
+    )
+    cols = pd.MultiIndex.from_tuples(
+        [("a", "foo"), ("a", "bar"), ("b", "foo"), ("b", "bah")], names=["lvl0", "lvl1"]
+    )
+    df = DataFrame(1, index=idx, columns=cols).sort_index().sort_index(axis=1)
+
+    mask = df[("a", "foo")] == 1
+    expected_mask = mask.copy()
+    result = df.loc[pd.IndexSlice[mask, :, ["C1", "C3"]], :]
+    expected = df.loc[pd.IndexSlice[:, :, ["C1", "C3"]], :]
+    tm.assert_frame_equal(result, expected)
+    tm.assert_series_equal(mask, expected_mask)
+
+
+def test_loc_enlarging_with_dataframe(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]})
+    rhs = DataFrame({"b": [1, 2, 3], "c": [4, 5, 6]})
+    rhs_orig = rhs.copy()
+    df.loc[:, ["b", "c"]] = rhs
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "b"), get_array(rhs, "b"))
+        assert np.shares_memory(get_array(df, "c"), get_array(rhs, "c"))
+        assert not df._mgr._has_no_reference(1)
+    else:
+        assert not np.shares_memory(get_array(df, "b"), get_array(rhs, "b"))
+
+    df.iloc[0, 1] = 100
+    tm.assert_frame_equal(rhs, rhs_orig)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_internals.py

@@ -0,0 +1,151 @@
+import numpy as np
+import pytest
+
+import pandas.util._test_decorators as td
+
+import pandas as pd
+from pandas import DataFrame
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+@td.skip_array_manager_invalid_test
+def test_consolidate(using_copy_on_write):
+    # create unconsolidated DataFrame
+    df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]})
+    df["c"] = [4, 5, 6]
+
+    # take a viewing subset
+    subset = df[:]
+
+    # each block of subset references a block of df
+    assert all(blk.refs.has_reference() for blk in subset._mgr.blocks)
+
+    # consolidate the two int64 blocks
+    subset._consolidate_inplace()
+
+    # the float64 block still references the parent one because it still a view
+    assert subset._mgr.blocks[0].refs.has_reference()
+    # equivalent of assert np.shares_memory(df["b"].values, subset["b"].values)
+    # but avoids caching df["b"]
+    assert np.shares_memory(get_array(df, "b"), get_array(subset, "b"))
+
+    # the new consolidated int64 block does not reference another
+    assert not subset._mgr.blocks[1].refs.has_reference()
+
+    # the parent dataframe now also only is linked for the float column
+    assert not df._mgr.blocks[0].refs.has_reference()
+    assert df._mgr.blocks[1].refs.has_reference()
+    assert not df._mgr.blocks[2].refs.has_reference()
+
+    # and modifying subset still doesn't modify parent
+    if using_copy_on_write:
+        subset.iloc[0, 1] = 0.0
+        assert not df._mgr.blocks[1].refs.has_reference()
+        assert df.loc[0, "b"] == 0.1
+
+
+@pytest.mark.single_cpu
+@td.skip_array_manager_invalid_test
+def test_switch_options():
+    # ensure we can switch the value of the option within one session
+    # (assuming data is constructed after switching)
+
+    # using the option_context to ensure we set back to global option value
+    # after running the test
+    with pd.option_context("mode.copy_on_write", False):
+        df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]})
+        subset = df[:]
+        subset.iloc[0, 0] = 0
+        # df updated with CoW disabled
+        assert df.iloc[0, 0] == 0
+
+        pd.options.mode.copy_on_write = True
+        df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]})
+        subset = df[:]
+        subset.iloc[0, 0] = 0
+        # df not updated with CoW enabled
+        assert df.iloc[0, 0] == 1
+
+        pd.options.mode.copy_on_write = False
+        df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]})
+        subset = df[:]
+        subset.iloc[0, 0] = 0
+        # df updated with CoW disabled
+        assert df.iloc[0, 0] == 0
+
+
+@td.skip_array_manager_invalid_test
+@pytest.mark.parametrize("dtype", [np.intp, np.int8])
+@pytest.mark.parametrize(
+    "locs, arr",
+    [
+        ([0], np.array([-1, -2, -3])),
+        ([1], np.array([-1, -2, -3])),
+        ([5], np.array([-1, -2, -3])),
+        ([0, 1], np.array([[-1, -2, -3], [-4, -5, -6]]).T),
+        ([0, 2], np.array([[-1, -2, -3], [-4, -5, -6]]).T),
+        ([0, 1, 2], np.array([[-1, -2, -3], [-4, -5, -6], [-4, -5, -6]]).T),
+        ([1, 2], np.array([[-1, -2, -3], [-4, -5, -6]]).T),
+        ([1, 3], np.array([[-1, -2, -3], [-4, -5, -6]]).T),
+        ([1, 3], np.array([[-1, -2, -3], [-4, -5, -6]]).T),
+    ],
+)
+def test_iset_splits_blocks_inplace(using_copy_on_write, locs, arr, dtype):
+    # Nothing currently calls iset with
+    # more than 1 loc with inplace=True (only happens with inplace=False)
+    # but ensure that it works
+    df = DataFrame(
+        {
+            "a": [1, 2, 3],
+            "b": [4, 5, 6],
+            "c": [7, 8, 9],
+            "d": [10, 11, 12],
+            "e": [13, 14, 15],
+            "f": ["a", "b", "c"],
+        },
+    )
+    arr = arr.astype(dtype)
+    df_orig = df.copy()
+    df2 = df.copy(deep=None)  # Trigger a CoW (if enabled, otherwise makes copy)
+    df2._mgr.iset(locs, arr, inplace=True)
+
+    tm.assert_frame_equal(df, df_orig)
+
+    if using_copy_on_write:
+        for i, col in enumerate(df.columns):
+            if i not in locs:
+                assert np.shares_memory(get_array(df, col), get_array(df2, col))
+    else:
+        for col in df.columns:
+            assert not np.shares_memory(get_array(df, col), get_array(df2, col))
+
+
+def test_exponential_backoff():
+    # GH#55518
+    df = DataFrame({"a": [1, 2, 3]})
+    for i in range(490):
+        df.copy(deep=False)
+
+    assert len(df._mgr.blocks[0].refs.referenced_blocks) == 491
+
+    df = DataFrame({"a": [1, 2, 3]})
+    dfs = [df.copy(deep=False) for i in range(510)]
+
+    for i in range(20):
+        df.copy(deep=False)
+    assert len(df._mgr.blocks[0].refs.referenced_blocks) == 531
+    assert df._mgr.blocks[0].refs.clear_counter == 1000
+
+    for i in range(500):
+        df.copy(deep=False)
+
+    # Don't reduce since we still have over 500 objects alive
+    assert df._mgr.blocks[0].refs.clear_counter == 1000
+
+    dfs = dfs[:300]
+    for i in range(500):
+        df.copy(deep=False)
+
+    # Reduce since there are less than 500 objects alive
+    assert df._mgr.blocks[0].refs.clear_counter == 500

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_interp_fillna.py

@@ -0,0 +1,432 @@
+import numpy as np
+import pytest
+
+from pandas import (
+    NA,
+    ArrowDtype,
+    DataFrame,
+    Interval,
+    NaT,
+    Series,
+    Timestamp,
+    interval_range,
+    option_context,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+@pytest.mark.parametrize("method", ["pad", "nearest", "linear"])
+def test_interpolate_no_op(using_copy_on_write, method):
+    df = DataFrame({"a": [1, 2]})
+    df_orig = df.copy()
+
+    warn = None
+    if method == "pad":
+        warn = FutureWarning
+    msg = "DataFrame.interpolate with method=pad is deprecated"
+    with tm.assert_produces_warning(warn, match=msg):
+        result = df.interpolate(method=method)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+
+    result.iloc[0, 0] = 100
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize("func", ["ffill", "bfill"])
+def test_interp_fill_functions(using_copy_on_write, func):
+    # Check that these takes the same code paths as interpolate
+    df = DataFrame({"a": [1, 2]})
+    df_orig = df.copy()
+
+    result = getattr(df, func)()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+
+    result.iloc[0, 0] = 100
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize("func", ["ffill", "bfill"])
+@pytest.mark.parametrize(
+    "vals", [[1, np.nan, 2], [Timestamp("2019-12-31"), NaT, Timestamp("2020-12-31")]]
+)
+def test_interpolate_triggers_copy(using_copy_on_write, vals, func):
+    df = DataFrame({"a": vals})
+    result = getattr(df, func)()
+
+    assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    if using_copy_on_write:
+        # Check that we don't have references when triggering a copy
+        assert result._mgr._has_no_reference(0)
+
+
+@pytest.mark.parametrize(
+    "vals", [[1, np.nan, 2], [Timestamp("2019-12-31"), NaT, Timestamp("2020-12-31")]]
+)
+def test_interpolate_inplace_no_reference_no_copy(using_copy_on_write, vals):
+    df = DataFrame({"a": vals})
+    arr = get_array(df, "a")
+    df.interpolate(method="linear", inplace=True)
+
+    assert np.shares_memory(arr, get_array(df, "a"))
+    if using_copy_on_write:
+        # Check that we don't have references when triggering a copy
+        assert df._mgr._has_no_reference(0)
+
+
+@pytest.mark.parametrize(
+    "vals", [[1, np.nan, 2], [Timestamp("2019-12-31"), NaT, Timestamp("2020-12-31")]]
+)
+def test_interpolate_inplace_with_refs(using_copy_on_write, vals, warn_copy_on_write):
+    df = DataFrame({"a": [1, np.nan, 2]})
+    df_orig = df.copy()
+    arr = get_array(df, "a")
+    view = df[:]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.interpolate(method="linear", inplace=True)
+
+    if using_copy_on_write:
+        # Check that copy was triggered in interpolate and that we don't
+        # have any references left
+        assert not np.shares_memory(arr, get_array(df, "a"))
+        tm.assert_frame_equal(df_orig, view)
+        assert df._mgr._has_no_reference(0)
+        assert view._mgr._has_no_reference(0)
+    else:
+        assert np.shares_memory(arr, get_array(df, "a"))
+
+
+@pytest.mark.parametrize("func", ["ffill", "bfill"])
+@pytest.mark.parametrize("dtype", ["float64", "Float64"])
+def test_interp_fill_functions_inplace(
+    using_copy_on_write, func, warn_copy_on_write, dtype
+):
+    # Check that these takes the same code paths as interpolate
+    df = DataFrame({"a": [1, np.nan, 2]}, dtype=dtype)
+    df_orig = df.copy()
+    arr = get_array(df, "a")
+    view = df[:]
+
+    with tm.assert_cow_warning(warn_copy_on_write and dtype == "float64"):
+        getattr(df, func)(inplace=True)
+
+    if using_copy_on_write:
+        # Check that copy was triggered in interpolate and that we don't
+        # have any references left
+        assert not np.shares_memory(arr, get_array(df, "a"))
+        tm.assert_frame_equal(df_orig, view)
+        assert df._mgr._has_no_reference(0)
+        assert view._mgr._has_no_reference(0)
+    else:
+        assert np.shares_memory(arr, get_array(df, "a")) is (dtype == "float64")
+
+
+def test_interpolate_cleaned_fill_method(using_copy_on_write):
+    # Check that "method is set to None" case works correctly
+    df = DataFrame({"a": ["a", np.nan, "c"], "b": 1})
+    df_orig = df.copy()
+
+    msg = "DataFrame.interpolate with object dtype"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = df.interpolate(method="linear")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+
+    result.iloc[0, 0] = Timestamp("2021-12-31")
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_interpolate_object_convert_no_op(using_copy_on_write):
+    df = DataFrame({"a": ["a", "b", "c"], "b": 1})
+    arr_a = get_array(df, "a")
+    msg = "DataFrame.interpolate with method=pad is deprecated"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.interpolate(method="pad", inplace=True)
+
+    # Now CoW makes a copy, it should not!
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+        assert np.shares_memory(arr_a, get_array(df, "a"))
+
+
+def test_interpolate_object_convert_copies(using_copy_on_write):
+    df = DataFrame({"a": Series([1, 2], dtype=object), "b": 1})
+    arr_a = get_array(df, "a")
+    msg = "DataFrame.interpolate with method=pad is deprecated"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.interpolate(method="pad", inplace=True)
+
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+        assert not np.shares_memory(arr_a, get_array(df, "a"))
+
+
+def test_interpolate_downcast(using_copy_on_write):
+    df = DataFrame({"a": [1, np.nan, 2.5], "b": 1})
+    arr_a = get_array(df, "a")
+    msg = "DataFrame.interpolate with method=pad is deprecated"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.interpolate(method="pad", inplace=True, downcast="infer")
+
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+    assert np.shares_memory(arr_a, get_array(df, "a"))
+
+
+def test_interpolate_downcast_reference_triggers_copy(using_copy_on_write):
+    df = DataFrame({"a": [1, np.nan, 2.5], "b": 1})
+    df_orig = df.copy()
+    arr_a = get_array(df, "a")
+    view = df[:]
+    msg = "DataFrame.interpolate with method=pad is deprecated"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.interpolate(method="pad", inplace=True, downcast="infer")
+
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+        assert not np.shares_memory(arr_a, get_array(df, "a"))
+        tm.assert_frame_equal(df_orig, view)
+    else:
+        tm.assert_frame_equal(df, view)
+
+
+def test_fillna(using_copy_on_write):
+    df = DataFrame({"a": [1.5, np.nan], "b": 1})
+    df_orig = df.copy()
+
+    df2 = df.fillna(5.5)
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+    else:
+        assert not np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+
+    df2.iloc[0, 1] = 100
+    tm.assert_frame_equal(df_orig, df)
+
+
+def test_fillna_dict(using_copy_on_write):
+    df = DataFrame({"a": [1.5, np.nan], "b": 1})
+    df_orig = df.copy()
+
+    df2 = df.fillna({"a": 100.5})
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+    else:
+        assert not np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+
+    df2.iloc[0, 1] = 100
+    tm.assert_frame_equal(df_orig, df)
+
+
+@pytest.mark.parametrize("downcast", [None, False])
+def test_fillna_inplace(using_copy_on_write, downcast):
+    df = DataFrame({"a": [1.5, np.nan], "b": 1})
+    arr_a = get_array(df, "a")
+    arr_b = get_array(df, "b")
+
+    msg = "The 'downcast' keyword in fillna is deprecated"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.fillna(5.5, inplace=True, downcast=downcast)
+    assert np.shares_memory(get_array(df, "a"), arr_a)
+    assert np.shares_memory(get_array(df, "b"), arr_b)
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+        assert df._mgr._has_no_reference(1)
+
+
+def test_fillna_inplace_reference(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1.5, np.nan], "b": 1})
+    df_orig = df.copy()
+    arr_a = get_array(df, "a")
+    arr_b = get_array(df, "b")
+    view = df[:]
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.fillna(5.5, inplace=True)
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), arr_a)
+        assert np.shares_memory(get_array(df, "b"), arr_b)
+        assert view._mgr._has_no_reference(0)
+        assert df._mgr._has_no_reference(0)
+        tm.assert_frame_equal(view, df_orig)
+    else:
+        assert np.shares_memory(get_array(df, "a"), arr_a)
+        assert np.shares_memory(get_array(df, "b"), arr_b)
+    expected = DataFrame({"a": [1.5, 5.5], "b": 1})
+    tm.assert_frame_equal(df, expected)
+
+
+def test_fillna_interval_inplace_reference(using_copy_on_write, warn_copy_on_write):
+    # Set dtype explicitly to avoid implicit cast when setting nan
+    ser = Series(
+        interval_range(start=0, end=5), name="a", dtype="interval[float64, right]"
+    )
+    ser.iloc[1] = np.nan
+
+    ser_orig = ser.copy()
+    view = ser[:]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser.fillna(value=Interval(left=0, right=5), inplace=True)
+
+    if using_copy_on_write:
+        assert not np.shares_memory(
+            get_array(ser, "a").left.values, get_array(view, "a").left.values
+        )
+        tm.assert_series_equal(view, ser_orig)
+    else:
+        assert np.shares_memory(
+            get_array(ser, "a").left.values, get_array(view, "a").left.values
+        )
+
+
+def test_fillna_series_empty_arg(using_copy_on_write):
+    ser = Series([1, np.nan, 2])
+    ser_orig = ser.copy()
+    result = ser.fillna({})
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(ser), get_array(result))
+    else:
+        assert not np.shares_memory(get_array(ser), get_array(result))
+
+    ser.iloc[0] = 100.5
+    tm.assert_series_equal(ser_orig, result)
+
+
+def test_fillna_series_empty_arg_inplace(using_copy_on_write):
+    ser = Series([1, np.nan, 2])
+    arr = get_array(ser)
+    ser.fillna({}, inplace=True)
+
+    assert np.shares_memory(get_array(ser), arr)
+    if using_copy_on_write:
+        assert ser._mgr._has_no_reference(0)
+
+
+def test_fillna_ea_noop_shares_memory(
+    using_copy_on_write, any_numeric_ea_and_arrow_dtype
+):
+    df = DataFrame({"a": [1, NA, 3], "b": 1}, dtype=any_numeric_ea_and_arrow_dtype)
+    df_orig = df.copy()
+    df2 = df.fillna(100)
+
+    assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+        assert not df2._mgr._has_no_reference(1)
+    elif isinstance(df.dtypes.iloc[0], ArrowDtype):
+        # arrow is immutable, so no-ops do not need to copy underlying array
+        assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+    else:
+        assert not np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+
+    tm.assert_frame_equal(df_orig, df)
+
+    df2.iloc[0, 1] = 100
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+        assert df2._mgr._has_no_reference(1)
+        assert df._mgr._has_no_reference(1)
+    tm.assert_frame_equal(df_orig, df)
+
+
+def test_fillna_inplace_ea_noop_shares_memory(
+    using_copy_on_write, warn_copy_on_write, any_numeric_ea_and_arrow_dtype
+):
+    df = DataFrame({"a": [1, NA, 3], "b": 1}, dtype=any_numeric_ea_and_arrow_dtype)
+    df_orig = df.copy()
+    view = df[:]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.fillna(100, inplace=True)
+
+    if isinstance(df["a"].dtype, ArrowDtype) or using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), get_array(view, "a"))
+    else:
+        # MaskedArray can actually respect inplace=True
+        assert np.shares_memory(get_array(df, "a"), get_array(view, "a"))
+
+    assert np.shares_memory(get_array(df, "b"), get_array(view, "b"))
+    if using_copy_on_write:
+        assert not df._mgr._has_no_reference(1)
+        assert not view._mgr._has_no_reference(1)
+
+    with tm.assert_cow_warning(
+        warn_copy_on_write and "pyarrow" not in any_numeric_ea_and_arrow_dtype
+    ):
+        df.iloc[0, 1] = 100
+    if isinstance(df["a"].dtype, ArrowDtype) or using_copy_on_write:
+        tm.assert_frame_equal(df_orig, view)
+    else:
+        # we actually have a view
+        tm.assert_frame_equal(df, view)
+
+
+def test_fillna_chained_assignment(using_copy_on_write):
+    df = DataFrame({"a": [1, np.nan, 2], "b": 1})
+    df_orig = df.copy()
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error():
+            df["a"].fillna(100, inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+
+        with tm.raises_chained_assignment_error():
+            df[["a"]].fillna(100, inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                df[["a"]].fillna(100, inplace=True)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                df[df.a > 5].fillna(100, inplace=True)
+
+        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+            df["a"].fillna(100, inplace=True)
+
+
+@pytest.mark.parametrize("func", ["interpolate", "ffill", "bfill"])
+def test_interpolate_chained_assignment(using_copy_on_write, func):
+    df = DataFrame({"a": [1, np.nan, 2], "b": 1})
+    df_orig = df.copy()
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error():
+            getattr(df["a"], func)(inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+
+        with tm.raises_chained_assignment_error():
+            getattr(df[["a"]], func)(inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+            getattr(df["a"], func)(inplace=True)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                getattr(df[["a"]], func)(inplace=True)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                getattr(df[df["a"] > 1], func)(inplace=True)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_methods.py

@@ -0,0 +1,2055 @@
+import numpy as np
+import pytest
+
+from pandas.errors import SettingWithCopyWarning
+
+import pandas as pd
+from pandas import (
+    DataFrame,
+    Index,
+    MultiIndex,
+    Period,
+    Series,
+    Timestamp,
+    date_range,
+    option_context,
+    period_range,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+def test_copy(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_copy = df.copy()
+
+    # the deep copy by defaults takes a shallow copy of the Index
+    assert df_copy.index is not df.index
+    assert df_copy.columns is not df.columns
+    assert df_copy.index.is_(df.index)
+    assert df_copy.columns.is_(df.columns)
+
+    # the deep copy doesn't share memory
+    assert not np.shares_memory(get_array(df_copy, "a"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert not df_copy._mgr.blocks[0].refs.has_reference()
+        assert not df_copy._mgr.blocks[1].refs.has_reference()
+
+    # mutating copy doesn't mutate original
+    df_copy.iloc[0, 0] = 0
+    assert df.iloc[0, 0] == 1
+
+
+def test_copy_shallow(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_copy = df.copy(deep=False)
+
+    # the shallow copy also makes a shallow copy of the index
+    if using_copy_on_write:
+        assert df_copy.index is not df.index
+        assert df_copy.columns is not df.columns
+        assert df_copy.index.is_(df.index)
+        assert df_copy.columns.is_(df.columns)
+    else:
+        assert df_copy.index is df.index
+        assert df_copy.columns is df.columns
+
+    # the shallow copy still shares memory
+    assert np.shares_memory(get_array(df_copy, "a"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert df_copy._mgr.blocks[0].refs.has_reference()
+        assert df_copy._mgr.blocks[1].refs.has_reference()
+
+    if using_copy_on_write:
+        # mutating shallow copy doesn't mutate original
+        df_copy.iloc[0, 0] = 0
+        assert df.iloc[0, 0] == 1
+        # mutating triggered a copy-on-write -> no longer shares memory
+        assert not np.shares_memory(get_array(df_copy, "a"), get_array(df, "a"))
+        # but still shares memory for the other columns/blocks
+        assert np.shares_memory(get_array(df_copy, "c"), get_array(df, "c"))
+    else:
+        # mutating shallow copy does mutate original
+        with tm.assert_cow_warning(warn_copy_on_write):
+            df_copy.iloc[0, 0] = 0
+        assert df.iloc[0, 0] == 0
+        # and still shares memory
+        assert np.shares_memory(get_array(df_copy, "a"), get_array(df, "a"))
+
+
+@pytest.mark.parametrize("copy", [True, None, False])
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda df, copy: df.rename(columns=str.lower, copy=copy),
+        lambda df, copy: df.reindex(columns=["a", "c"], copy=copy),
+        lambda df, copy: df.reindex_like(df, copy=copy),
+        lambda df, copy: df.align(df, copy=copy)[0],
+        lambda df, copy: df.set_axis(["a", "b", "c"], axis="index", copy=copy),
+        lambda df, copy: df.rename_axis(index="test", copy=copy),
+        lambda df, copy: df.rename_axis(columns="test", copy=copy),
+        lambda df, copy: df.astype({"b": "int64"}, copy=copy),
+        # lambda df, copy: df.swaplevel(0, 0, copy=copy),
+        lambda df, copy: df.swapaxes(0, 0, copy=copy),
+        lambda df, copy: df.truncate(0, 5, copy=copy),
+        lambda df, copy: df.infer_objects(copy=copy),
+        lambda df, copy: df.to_timestamp(copy=copy),
+        lambda df, copy: df.to_period(freq="D", copy=copy),
+        lambda df, copy: df.tz_localize("US/Central", copy=copy),
+        lambda df, copy: df.tz_convert("US/Central", copy=copy),
+        lambda df, copy: df.set_flags(allows_duplicate_labels=False, copy=copy),
+    ],
+    ids=[
+        "rename",
+        "reindex",
+        "reindex_like",
+        "align",
+        "set_axis",
+        "rename_axis0",
+        "rename_axis1",
+        "astype",
+        # "swaplevel",  # only series
+        "swapaxes",
+        "truncate",
+        "infer_objects",
+        "to_timestamp",
+        "to_period",
+        "tz_localize",
+        "tz_convert",
+        "set_flags",
+    ],
+)
+def test_methods_copy_keyword(
+    request, method, copy, using_copy_on_write, using_array_manager
+):
+    index = None
+    if "to_timestamp" in request.node.callspec.id:
+        index = period_range("2012-01-01", freq="D", periods=3)
+    elif "to_period" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3)
+    elif "tz_localize" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3)
+    elif "tz_convert" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3, tz="Europe/Brussels")
+
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}, index=index)
+
+    if "swapaxes" in request.node.callspec.id:
+        msg = "'DataFrame.swapaxes' is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            df2 = method(df, copy=copy)
+    else:
+        df2 = method(df, copy=copy)
+
+    share_memory = using_copy_on_write or copy is False
+
+    if request.node.callspec.id.startswith("reindex-"):
+        # TODO copy=False without CoW still returns a copy in this case
+        if not using_copy_on_write and not using_array_manager and copy is False:
+            share_memory = False
+
+    if share_memory:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+
+@pytest.mark.parametrize("copy", [True, None, False])
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda ser, copy: ser.rename(index={0: 100}, copy=copy),
+        lambda ser, copy: ser.rename(None, copy=copy),
+        lambda ser, copy: ser.reindex(index=ser.index, copy=copy),
+        lambda ser, copy: ser.reindex_like(ser, copy=copy),
+        lambda ser, copy: ser.align(ser, copy=copy)[0],
+        lambda ser, copy: ser.set_axis(["a", "b", "c"], axis="index", copy=copy),
+        lambda ser, copy: ser.rename_axis(index="test", copy=copy),
+        lambda ser, copy: ser.astype("int64", copy=copy),
+        lambda ser, copy: ser.swaplevel(0, 1, copy=copy),
+        lambda ser, copy: ser.swapaxes(0, 0, copy=copy),
+        lambda ser, copy: ser.truncate(0, 5, copy=copy),
+        lambda ser, copy: ser.infer_objects(copy=copy),
+        lambda ser, copy: ser.to_timestamp(copy=copy),
+        lambda ser, copy: ser.to_period(freq="D", copy=copy),
+        lambda ser, copy: ser.tz_localize("US/Central", copy=copy),
+        lambda ser, copy: ser.tz_convert("US/Central", copy=copy),
+        lambda ser, copy: ser.set_flags(allows_duplicate_labels=False, copy=copy),
+    ],
+    ids=[
+        "rename (dict)",
+        "rename",
+        "reindex",
+        "reindex_like",
+        "align",
+        "set_axis",
+        "rename_axis0",
+        "astype",
+        "swaplevel",
+        "swapaxes",
+        "truncate",
+        "infer_objects",
+        "to_timestamp",
+        "to_period",
+        "tz_localize",
+        "tz_convert",
+        "set_flags",
+    ],
+)
+def test_methods_series_copy_keyword(request, method, copy, using_copy_on_write):
+    index = None
+    if "to_timestamp" in request.node.callspec.id:
+        index = period_range("2012-01-01", freq="D", periods=3)
+    elif "to_period" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3)
+    elif "tz_localize" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3)
+    elif "tz_convert" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3, tz="Europe/Brussels")
+    elif "swaplevel" in request.node.callspec.id:
+        index = MultiIndex.from_arrays([[1, 2, 3], [4, 5, 6]])
+
+    ser = Series([1, 2, 3], index=index)
+
+    if "swapaxes" in request.node.callspec.id:
+        msg = "'Series.swapaxes' is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            ser2 = method(ser, copy=copy)
+    else:
+        ser2 = method(ser, copy=copy)
+
+    share_memory = using_copy_on_write or copy is False
+
+    if share_memory:
+        assert np.shares_memory(get_array(ser2), get_array(ser))
+    else:
+        assert not np.shares_memory(get_array(ser2), get_array(ser))
+
+
+@pytest.mark.parametrize("copy", [True, None, False])
+def test_transpose_copy_keyword(using_copy_on_write, copy, using_array_manager):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    result = df.transpose(copy=copy)
+    share_memory = using_copy_on_write or copy is False or copy is None
+    share_memory = share_memory and not using_array_manager
+
+    if share_memory:
+        assert np.shares_memory(get_array(df, "a"), get_array(result, 0))
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, 0))
+
+
+# -----------------------------------------------------------------------------
+# DataFrame methods returning new DataFrame using shallow copy
+
+
+def test_reset_index(using_copy_on_write):
+    # Case: resetting the index (i.e. adding a new column) + mutating the
+    # resulting dataframe
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}, index=[10, 11, 12]
+    )
+    df_orig = df.copy()
+    df2 = df.reset_index()
+    df2._mgr._verify_integrity()
+
+    if using_copy_on_write:
+        # still shares memory (df2 is a shallow copy)
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    # mutating df2 triggers a copy-on-write for that column / block
+    df2.iloc[0, 2] = 0
+    assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize("index", [pd.RangeIndex(0, 2), Index([1, 2])])
+def test_reset_index_series_drop(using_copy_on_write, index):
+    ser = Series([1, 2], index=index)
+    ser_orig = ser.copy()
+    ser2 = ser.reset_index(drop=True)
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(ser), get_array(ser2))
+        assert not ser._mgr._has_no_reference(0)
+    else:
+        assert not np.shares_memory(get_array(ser), get_array(ser2))
+
+    ser2.iloc[0] = 100
+    tm.assert_series_equal(ser, ser_orig)
+
+
+def test_groupby_column_index_in_references():
+    df = DataFrame(
+        {"A": ["a", "b", "c", "d"], "B": [1, 2, 3, 4], "C": ["a", "a", "b", "b"]}
+    )
+    df = df.set_index("A")
+    key = df["C"]
+    result = df.groupby(key, observed=True).sum()
+    expected = df.groupby("C", observed=True).sum()
+    tm.assert_frame_equal(result, expected)
+
+
+def test_rename_columns(using_copy_on_write):
+    # Case: renaming columns returns a new dataframe
+    # + afterwards modifying the result
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.rename(columns=str.upper)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "A"), get_array(df, "a"))
+    df2.iloc[0, 0] = 0
+    assert not np.shares_memory(get_array(df2, "A"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "C"), get_array(df, "c"))
+    expected = DataFrame({"A": [0, 2, 3], "B": [4, 5, 6], "C": [0.1, 0.2, 0.3]})
+    tm.assert_frame_equal(df2, expected)
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_rename_columns_modify_parent(using_copy_on_write):
+    # Case: renaming columns returns a new dataframe
+    # + afterwards modifying the original (parent) dataframe
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df2 = df.rename(columns=str.upper)
+    df2_orig = df2.copy()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "A"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "A"), get_array(df, "a"))
+    df.iloc[0, 0] = 0
+    assert not np.shares_memory(get_array(df2, "A"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "C"), get_array(df, "c"))
+    expected = DataFrame({"a": [0, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    tm.assert_frame_equal(df, expected)
+    tm.assert_frame_equal(df2, df2_orig)
+
+
+def test_pipe(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1.5})
+    df_orig = df.copy()
+
+    def testfunc(df):
+        return df
+
+    df2 = df.pipe(testfunc)
+
+    assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        expected = DataFrame({"a": [0, 2, 3], "b": 1.5})
+        tm.assert_frame_equal(df, expected)
+
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+
+
+def test_pipe_modify_df(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1.5})
+    df_orig = df.copy()
+
+    def testfunc(df):
+        df.iloc[0, 0] = 100
+        return df
+
+    df2 = df.pipe(testfunc)
+
+    assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        expected = DataFrame({"a": [100, 2, 3], "b": 1.5})
+        tm.assert_frame_equal(df, expected)
+
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+
+
+def test_reindex_columns(using_copy_on_write):
+    # Case: reindexing the column returns a new dataframe
+    # + afterwards modifying the result
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.reindex(columns=["a", "c"])
+
+    if using_copy_on_write:
+        # still shares memory (df2 is a shallow copy)
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    # mutating df2 triggers a copy-on-write for that column
+    df2.iloc[0, 0] = 0
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "index",
+    [
+        lambda idx: idx,
+        lambda idx: idx.view(),
+        lambda idx: idx.copy(),
+        lambda idx: list(idx),
+    ],
+    ids=["identical", "view", "copy", "values"],
+)
+def test_reindex_rows(index, using_copy_on_write):
+    # Case: reindexing the rows with an index that matches the current index
+    # can use a shallow copy
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.reindex(index=index(df.index))
+
+    if using_copy_on_write:
+        # still shares memory (df2 is a shallow copy)
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    # mutating df2 triggers a copy-on-write for that column
+    df2.iloc[0, 0] = 0
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_drop_on_column(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.drop(columns="a")
+    df2._mgr._verify_integrity()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    else:
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    df2.iloc[0, 0] = 0
+    assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_select_dtypes(using_copy_on_write):
+    # Case: selecting columns using `select_dtypes()` returns a new dataframe
+    # + afterwards modifying the result
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.select_dtypes("int64")
+    df2._mgr._verify_integrity()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column/block
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "filter_kwargs", [{"items": ["a"]}, {"like": "a"}, {"regex": "a"}]
+)
+def test_filter(using_copy_on_write, filter_kwargs):
+    # Case: selecting columns using `filter()` returns a new dataframe
+    # + afterwards modifying the result
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.filter(**filter_kwargs)
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column/block
+    if using_copy_on_write:
+        df2.iloc[0, 0] = 0
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_shift_no_op(using_copy_on_write):
+    df = DataFrame(
+        [[1, 2], [3, 4], [5, 6]],
+        index=date_range("2020-01-01", "2020-01-03"),
+        columns=["a", "b"],
+    )
+    df_orig = df.copy()
+    df2 = df.shift(periods=0)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+        assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+    tm.assert_frame_equal(df2, df_orig)
+
+
+def test_shift_index(using_copy_on_write):
+    df = DataFrame(
+        [[1, 2], [3, 4], [5, 6]],
+        index=date_range("2020-01-01", "2020-01-03"),
+        columns=["a", "b"],
+    )
+    df2 = df.shift(periods=1, axis=0)
+
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+
+def test_shift_rows_freq(using_copy_on_write):
+    df = DataFrame(
+        [[1, 2], [3, 4], [5, 6]],
+        index=date_range("2020-01-01", "2020-01-03"),
+        columns=["a", "b"],
+    )
+    df_orig = df.copy()
+    df_orig.index = date_range("2020-01-02", "2020-01-04")
+    df2 = df.shift(periods=1, freq="1D")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+    tm.assert_frame_equal(df2, df_orig)
+
+
+def test_shift_columns(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame(
+        [[1, 2], [3, 4], [5, 6]], columns=date_range("2020-01-01", "2020-01-02")
+    )
+    df2 = df.shift(periods=1, axis=1)
+
+    assert np.shares_memory(get_array(df2, "2020-01-02"), get_array(df, "2020-01-01"))
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(
+            get_array(df2, "2020-01-02"), get_array(df, "2020-01-01")
+        )
+        expected = DataFrame(
+            [[np.nan, 1], [np.nan, 3], [np.nan, 5]],
+            columns=date_range("2020-01-01", "2020-01-02"),
+        )
+        tm.assert_frame_equal(df2, expected)
+
+
+def test_pop(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    view_original = df[:]
+    result = df.pop("a")
+
+    assert np.shares_memory(result.values, get_array(view_original, "a"))
+    assert np.shares_memory(get_array(df, "b"), get_array(view_original, "b"))
+
+    if using_copy_on_write:
+        result.iloc[0] = 0
+        assert not np.shares_memory(result.values, get_array(view_original, "a"))
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "b"), get_array(view_original, "b"))
+        tm.assert_frame_equal(view_original, df_orig)
+    else:
+        expected = DataFrame({"a": [1, 2, 3], "b": [0, 5, 6], "c": [0.1, 0.2, 0.3]})
+        tm.assert_frame_equal(view_original, expected)
+
+
+@pytest.mark.parametrize(
+    "func",
+    [
+        lambda x, y: x.align(y),
+        lambda x, y: x.align(y.a, axis=0),
+        lambda x, y: x.align(y.a.iloc[slice(0, 1)], axis=1),
+    ],
+)
+def test_align_frame(using_copy_on_write, func):
+    df = DataFrame({"a": [1, 2, 3], "b": "a"})
+    df_orig = df.copy()
+    df_changed = df[["b", "a"]].copy()
+    df2, _ = func(df, df_changed)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_align_series(using_copy_on_write):
+    ser = Series([1, 2])
+    ser_orig = ser.copy()
+    ser_other = ser.copy()
+    ser2, ser_other_result = ser.align(ser_other)
+
+    if using_copy_on_write:
+        assert np.shares_memory(ser2.values, ser.values)
+        assert np.shares_memory(ser_other_result.values, ser_other.values)
+    else:
+        assert not np.shares_memory(ser2.values, ser.values)
+        assert not np.shares_memory(ser_other_result.values, ser_other.values)
+
+    ser2.iloc[0] = 0
+    ser_other_result.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(ser2.values, ser.values)
+        assert not np.shares_memory(ser_other_result.values, ser_other.values)
+    tm.assert_series_equal(ser, ser_orig)
+    tm.assert_series_equal(ser_other, ser_orig)
+
+
+def test_align_copy_false(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    df_orig = df.copy()
+    df2, df3 = df.align(df, copy=False)
+
+    assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+    assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    if using_copy_on_write:
+        df2.loc[0, "a"] = 0
+        tm.assert_frame_equal(df, df_orig)  # Original is unchanged
+
+        df3.loc[0, "a"] = 0
+        tm.assert_frame_equal(df, df_orig)  # Original is unchanged
+
+
+def test_align_with_series_copy_false(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    ser = Series([1, 2, 3], name="x")
+    ser_orig = ser.copy()
+    df_orig = df.copy()
+    df2, ser2 = df.align(ser, copy=False, axis=0)
+
+    assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+    assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+    assert np.shares_memory(get_array(ser, "x"), get_array(ser2, "x"))
+
+    if using_copy_on_write:
+        df2.loc[0, "a"] = 0
+        tm.assert_frame_equal(df, df_orig)  # Original is unchanged
+
+        ser2.loc[0] = 0
+        tm.assert_series_equal(ser, ser_orig)  # Original is unchanged
+
+
+def test_to_frame(using_copy_on_write, warn_copy_on_write):
+    # Case: converting a Series to a DataFrame with to_frame
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+
+    df = ser[:].to_frame()
+
+    # currently this always returns a "view"
+    assert np.shares_memory(ser.values, get_array(df, 0))
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 0
+
+    if using_copy_on_write:
+        # mutating df triggers a copy-on-write for that column
+        assert not np.shares_memory(ser.values, get_array(df, 0))
+        tm.assert_series_equal(ser, ser_orig)
+    else:
+        # but currently select_dtypes() actually returns a view -> mutates parent
+        expected = ser_orig.copy()
+        expected.iloc[0] = 0
+        tm.assert_series_equal(ser, expected)
+
+    # modify original series -> don't modify dataframe
+    df = ser[:].to_frame()
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser.iloc[0] = 0
+
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, ser_orig.to_frame())
+    else:
+        expected = ser_orig.copy().to_frame()
+        expected.iloc[0, 0] = 0
+        tm.assert_frame_equal(df, expected)
+
+
+@pytest.mark.parametrize("ax", ["index", "columns"])
+def test_swapaxes_noop(using_copy_on_write, ax):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    df_orig = df.copy()
+    msg = "'DataFrame.swapaxes' is deprecated"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df2 = df.swapaxes(ax, ax)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column/block
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_swapaxes_single_block(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]}, index=["x", "y", "z"])
+    df_orig = df.copy()
+    msg = "'DataFrame.swapaxes' is deprecated"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df2 = df.swapaxes("index", "columns")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "x"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "x"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column/block
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "x"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_swapaxes_read_only_array():
+    df = DataFrame({"a": [1, 2], "b": 3})
+    msg = "'DataFrame.swapaxes' is deprecated"
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df = df.swapaxes(axis1="index", axis2="columns")
+    df.iloc[0, 0] = 100
+    expected = DataFrame({0: [100, 3], 1: [2, 3]}, index=["a", "b"])
+    tm.assert_frame_equal(df, expected)
+
+
+@pytest.mark.parametrize(
+    "method, idx",
+    [
+        (lambda df: df.copy(deep=False).copy(deep=False), 0),
+        (lambda df: df.reset_index().reset_index(), 2),
+        (lambda df: df.rename(columns=str.upper).rename(columns=str.lower), 0),
+        (lambda df: df.copy(deep=False).select_dtypes(include="number"), 0),
+    ],
+    ids=["shallow-copy", "reset_index", "rename", "select_dtypes"],
+)
+def test_chained_methods(request, method, idx, using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+
+    # when not using CoW, only the copy() variant actually gives a view
+    df2_is_view = not using_copy_on_write and request.node.callspec.id == "shallow-copy"
+
+    # modify df2 -> don't modify df
+    df2 = method(df)
+    with tm.assert_cow_warning(warn_copy_on_write and df2_is_view):
+        df2.iloc[0, idx] = 0
+    if not df2_is_view:
+        tm.assert_frame_equal(df, df_orig)
+
+    # modify df -> don't modify df2
+    df2 = method(df)
+    with tm.assert_cow_warning(warn_copy_on_write and df2_is_view):
+        df.iloc[0, 0] = 0
+    if not df2_is_view:
+        tm.assert_frame_equal(df2.iloc[:, idx:], df_orig)
+
+
+@pytest.mark.parametrize("obj", [Series([1, 2], name="a"), DataFrame({"a": [1, 2]})])
+def test_to_timestamp(using_copy_on_write, obj):
+    obj.index = Index([Period("2012-1-1", freq="D"), Period("2012-1-2", freq="D")])
+
+    obj_orig = obj.copy()
+    obj2 = obj.to_timestamp()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+    else:
+        assert not np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+
+    # mutating obj2 triggers a copy-on-write for that column / block
+    obj2.iloc[0] = 0
+    assert not np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+    tm.assert_equal(obj, obj_orig)
+
+
+@pytest.mark.parametrize("obj", [Series([1, 2], name="a"), DataFrame({"a": [1, 2]})])
+def test_to_period(using_copy_on_write, obj):
+    obj.index = Index([Timestamp("2019-12-31"), Timestamp("2020-12-31")])
+
+    obj_orig = obj.copy()
+    obj2 = obj.to_period(freq="Y")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+    else:
+        assert not np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+
+    # mutating obj2 triggers a copy-on-write for that column / block
+    obj2.iloc[0] = 0
+    assert not np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+    tm.assert_equal(obj, obj_orig)
+
+
+def test_set_index(using_copy_on_write):
+    # GH 49473
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.set_index("a")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+    else:
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+
+    # mutating df2 triggers a copy-on-write for that column / block
+    df2.iloc[0, 1] = 0
+    assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_set_index_mutating_parent_does_not_mutate_index():
+    df = DataFrame({"a": [1, 2, 3], "b": 1})
+    result = df.set_index("a")
+    expected = result.copy()
+
+    df.iloc[0, 0] = 100
+    tm.assert_frame_equal(result, expected)
+
+
+def test_add_prefix(using_copy_on_write):
+    # GH 49473
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.add_prefix("CoW_")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "CoW_a"), get_array(df, "a"))
+    df2.iloc[0, 0] = 0
+
+    assert not np.shares_memory(get_array(df2, "CoW_a"), get_array(df, "a"))
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "CoW_c"), get_array(df, "c"))
+    expected = DataFrame(
+        {"CoW_a": [0, 2, 3], "CoW_b": [4, 5, 6], "CoW_c": [0.1, 0.2, 0.3]}
+    )
+    tm.assert_frame_equal(df2, expected)
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_add_suffix(using_copy_on_write):
+    # GH 49473
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.add_suffix("_CoW")
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a_CoW"), get_array(df, "a"))
+    df2.iloc[0, 0] = 0
+    assert not np.shares_memory(get_array(df2, "a_CoW"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "c_CoW"), get_array(df, "c"))
+    expected = DataFrame(
+        {"a_CoW": [0, 2, 3], "b_CoW": [4, 5, 6], "c_CoW": [0.1, 0.2, 0.3]}
+    )
+    tm.assert_frame_equal(df2, expected)
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize("axis, val", [(0, 5.5), (1, np.nan)])
+def test_dropna(using_copy_on_write, axis, val):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, val, 6], "c": "d"})
+    df_orig = df.copy()
+    df2 = df.dropna(axis=axis)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize("val", [5, 5.5])
+def test_dropna_series(using_copy_on_write, val):
+    ser = Series([1, val, 4])
+    ser_orig = ser.copy()
+    ser2 = ser.dropna()
+
+    if using_copy_on_write:
+        assert np.shares_memory(ser2.values, ser.values)
+    else:
+        assert not np.shares_memory(ser2.values, ser.values)
+
+    ser2.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(ser2.values, ser.values)
+    tm.assert_series_equal(ser, ser_orig)
+
+
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda df: df.head(),
+        lambda df: df.head(2),
+        lambda df: df.tail(),
+        lambda df: df.tail(3),
+    ],
+)
+def test_head_tail(method, using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = method(df)
+    df2._mgr._verify_integrity()
+
+    if using_copy_on_write:
+        # We are explicitly deviating for CoW here to make an eager copy (avoids
+        # tracking references for very cheap ops)
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+
+    # modify df2 to trigger CoW for that block
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        # without CoW enabled, head and tail return views. Mutating df2 also mutates df.
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        with tm.assert_cow_warning(warn_copy_on_write):
+            df2.iloc[0, 0] = 1
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_infer_objects(using_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": "c", "c": 1, "d": "x"})
+    df_orig = df.copy()
+    df2 = df.infer_objects()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+
+    df2.iloc[0, 0] = 0
+    df2.iloc[0, 1] = "d"
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_infer_objects_no_reference(using_copy_on_write):
+    df = DataFrame(
+        {
+            "a": [1, 2],
+            "b": "c",
+            "c": 1,
+            "d": Series(
+                [Timestamp("2019-12-31"), Timestamp("2020-12-31")], dtype="object"
+            ),
+            "e": "b",
+        }
+    )
+    df = df.infer_objects()
+
+    arr_a = get_array(df, "a")
+    arr_b = get_array(df, "b")
+    arr_d = get_array(df, "d")
+
+    df.iloc[0, 0] = 0
+    df.iloc[0, 1] = "d"
+    df.iloc[0, 3] = Timestamp("2018-12-31")
+    if using_copy_on_write:
+        assert np.shares_memory(arr_a, get_array(df, "a"))
+        # TODO(CoW): Block splitting causes references here
+        assert not np.shares_memory(arr_b, get_array(df, "b"))
+        assert np.shares_memory(arr_d, get_array(df, "d"))
+
+
+def test_infer_objects_reference(using_copy_on_write):
+    df = DataFrame(
+        {
+            "a": [1, 2],
+            "b": "c",
+            "c": 1,
+            "d": Series(
+                [Timestamp("2019-12-31"), Timestamp("2020-12-31")], dtype="object"
+            ),
+        }
+    )
+    view = df[:]  # noqa: F841
+    df = df.infer_objects()
+
+    arr_a = get_array(df, "a")
+    arr_b = get_array(df, "b")
+    arr_d = get_array(df, "d")
+
+    df.iloc[0, 0] = 0
+    df.iloc[0, 1] = "d"
+    df.iloc[0, 3] = Timestamp("2018-12-31")
+    if using_copy_on_write:
+        assert not np.shares_memory(arr_a, get_array(df, "a"))
+        assert not np.shares_memory(arr_b, get_array(df, "b"))
+        assert np.shares_memory(arr_d, get_array(df, "d"))
+
+
+@pytest.mark.parametrize(
+    "kwargs",
+    [
+        {"before": "a", "after": "b", "axis": 1},
+        {"before": 0, "after": 1, "axis": 0},
+    ],
+)
+def test_truncate(using_copy_on_write, kwargs):
+    df = DataFrame({"a": [1, 2, 3], "b": 1, "c": 2})
+    df_orig = df.copy()
+    df2 = df.truncate(**kwargs)
+    df2._mgr._verify_integrity()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize("method", ["assign", "drop_duplicates"])
+def test_assign_drop_duplicates(using_copy_on_write, method):
+    df = DataFrame({"a": [1, 2, 3]})
+    df_orig = df.copy()
+    df2 = getattr(df, method)()
+    df2._mgr._verify_integrity()
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize("obj", [Series([1, 2]), DataFrame({"a": [1, 2]})])
+def test_take(using_copy_on_write, obj):
+    # Check that no copy is made when we take all rows in original order
+    obj_orig = obj.copy()
+    obj2 = obj.take([0, 1])
+
+    if using_copy_on_write:
+        assert np.shares_memory(obj2.values, obj.values)
+    else:
+        assert not np.shares_memory(obj2.values, obj.values)
+
+    obj2.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(obj2.values, obj.values)
+    tm.assert_equal(obj, obj_orig)
+
+
+@pytest.mark.parametrize("obj", [Series([1, 2]), DataFrame({"a": [1, 2]})])
+def test_between_time(using_copy_on_write, obj):
+    obj.index = date_range("2018-04-09", periods=2, freq="1D20min")
+    obj_orig = obj.copy()
+    obj2 = obj.between_time("0:00", "1:00")
+
+    if using_copy_on_write:
+        assert np.shares_memory(obj2.values, obj.values)
+    else:
+        assert not np.shares_memory(obj2.values, obj.values)
+
+    obj2.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(obj2.values, obj.values)
+    tm.assert_equal(obj, obj_orig)
+
+
+def test_reindex_like(using_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": "a"})
+    other = DataFrame({"b": "a", "a": [1, 2]})
+
+    df_orig = df.copy()
+    df2 = df.reindex_like(other)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 1] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_sort_index(using_copy_on_write):
+    # GH 49473
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+    ser2 = ser.sort_index()
+
+    if using_copy_on_write:
+        assert np.shares_memory(ser.values, ser2.values)
+    else:
+        assert not np.shares_memory(ser.values, ser2.values)
+
+    # mutating ser triggers a copy-on-write for the column / block
+    ser2.iloc[0] = 0
+    assert not np.shares_memory(ser2.values, ser.values)
+    tm.assert_series_equal(ser, ser_orig)
+
+
+@pytest.mark.parametrize(
+    "obj, kwargs",
+    [(Series([1, 2, 3], name="a"), {}), (DataFrame({"a": [1, 2, 3]}), {"by": "a"})],
+)
+def test_sort_values(using_copy_on_write, obj, kwargs):
+    obj_orig = obj.copy()
+    obj2 = obj.sort_values(**kwargs)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+    else:
+        assert not np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+
+    # mutating df triggers a copy-on-write for the column / block
+    obj2.iloc[0] = 0
+    assert not np.shares_memory(get_array(obj2, "a"), get_array(obj, "a"))
+    tm.assert_equal(obj, obj_orig)
+
+
+@pytest.mark.parametrize(
+    "obj, kwargs",
+    [(Series([1, 2, 3], name="a"), {}), (DataFrame({"a": [1, 2, 3]}), {"by": "a"})],
+)
+def test_sort_values_inplace(using_copy_on_write, obj, kwargs, warn_copy_on_write):
+    obj_orig = obj.copy()
+    view = obj[:]
+    obj.sort_values(inplace=True, **kwargs)
+
+    assert np.shares_memory(get_array(obj, "a"), get_array(view, "a"))
+
+    # mutating obj triggers a copy-on-write for the column / block
+    with tm.assert_cow_warning(warn_copy_on_write):
+        obj.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(obj, "a"), get_array(view, "a"))
+        tm.assert_equal(view, obj_orig)
+    else:
+        assert np.shares_memory(get_array(obj, "a"), get_array(view, "a"))
+
+
+@pytest.mark.parametrize("decimals", [-1, 0, 1])
+def test_round(using_copy_on_write, warn_copy_on_write, decimals):
+    df = DataFrame({"a": [1, 2], "b": "c"})
+    df_orig = df.copy()
+    df2 = df.round(decimals=decimals)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        # TODO: Make inplace by using out parameter of ndarray.round?
+        if decimals >= 0:
+            # Ensure lazy copy if no-op
+            assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+        else:
+            assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 1] = "d"
+    df2.iloc[0, 0] = 4
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_reorder_levels(using_copy_on_write):
+    index = MultiIndex.from_tuples(
+        [(1, 1), (1, 2), (2, 1), (2, 2)], names=["one", "two"]
+    )
+    df = DataFrame({"a": [1, 2, 3, 4]}, index=index)
+    df_orig = df.copy()
+    df2 = df.reorder_levels(order=["two", "one"])
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_series_reorder_levels(using_copy_on_write):
+    index = MultiIndex.from_tuples(
+        [(1, 1), (1, 2), (2, 1), (2, 2)], names=["one", "two"]
+    )
+    ser = Series([1, 2, 3, 4], index=index)
+    ser_orig = ser.copy()
+    ser2 = ser.reorder_levels(order=["two", "one"])
+
+    if using_copy_on_write:
+        assert np.shares_memory(ser2.values, ser.values)
+    else:
+        assert not np.shares_memory(ser2.values, ser.values)
+
+    ser2.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(ser2.values, ser.values)
+    tm.assert_series_equal(ser, ser_orig)
+
+
+@pytest.mark.parametrize("obj", [Series([1, 2, 3]), DataFrame({"a": [1, 2, 3]})])
+def test_swaplevel(using_copy_on_write, obj):
+    index = MultiIndex.from_tuples([(1, 1), (1, 2), (2, 1)], names=["one", "two"])
+    obj.index = index
+    obj_orig = obj.copy()
+    obj2 = obj.swaplevel()
+
+    if using_copy_on_write:
+        assert np.shares_memory(obj2.values, obj.values)
+    else:
+        assert not np.shares_memory(obj2.values, obj.values)
+
+    obj2.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(obj2.values, obj.values)
+    tm.assert_equal(obj, obj_orig)
+
+
+def test_frame_set_axis(using_copy_on_write):
+    # GH 49473
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
+    df_orig = df.copy()
+    df2 = df.set_axis(["a", "b", "c"], axis="index")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column / block
+    df2.iloc[0, 0] = 0
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_series_set_axis(using_copy_on_write):
+    # GH 49473
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+    ser2 = ser.set_axis(["a", "b", "c"], axis="index")
+
+    if using_copy_on_write:
+        assert np.shares_memory(ser, ser2)
+    else:
+        assert not np.shares_memory(ser, ser2)
+
+    # mutating ser triggers a copy-on-write for the column / block
+    ser2.iloc[0] = 0
+    assert not np.shares_memory(ser2, ser)
+    tm.assert_series_equal(ser, ser_orig)
+
+
+def test_set_flags(using_copy_on_write, warn_copy_on_write):
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+    ser2 = ser.set_flags(allows_duplicate_labels=False)
+
+    assert np.shares_memory(ser, ser2)
+
+    # mutating ser triggers a copy-on-write for the column / block
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser2.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(ser2, ser)
+        tm.assert_series_equal(ser, ser_orig)
+    else:
+        assert np.shares_memory(ser2, ser)
+        expected = Series([0, 2, 3])
+        tm.assert_series_equal(ser, expected)
+
+
+@pytest.mark.parametrize("kwargs", [{"mapper": "test"}, {"index": "test"}])
+def test_rename_axis(using_copy_on_write, kwargs):
+    df = DataFrame({"a": [1, 2, 3, 4]}, index=Index([1, 2, 3, 4], name="a"))
+    df_orig = df.copy()
+    df2 = df.rename_axis(**kwargs)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    df2.iloc[0, 0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize(
+    "func, tz", [("tz_convert", "Europe/Berlin"), ("tz_localize", None)]
+)
+def test_tz_convert_localize(using_copy_on_write, func, tz):
+    # GH 49473
+    ser = Series(
+        [1, 2], index=date_range(start="2014-08-01 09:00", freq="h", periods=2, tz=tz)
+    )
+    ser_orig = ser.copy()
+    ser2 = getattr(ser, func)("US/Central")
+
+    if using_copy_on_write:
+        assert np.shares_memory(ser.values, ser2.values)
+    else:
+        assert not np.shares_memory(ser.values, ser2.values)
+
+    # mutating ser triggers a copy-on-write for the column / block
+    ser2.iloc[0] = 0
+    assert not np.shares_memory(ser2.values, ser.values)
+    tm.assert_series_equal(ser, ser_orig)
+
+
+def test_droplevel(using_copy_on_write):
+    # GH 49473
+    index = MultiIndex.from_tuples([(1, 1), (1, 2), (2, 1)], names=["one", "two"])
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]}, index=index)
+    df_orig = df.copy()
+    df2 = df.droplevel(0)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "c"), get_array(df, "c"))
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column / block
+    df2.iloc[0, 0] = 0
+
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "b"), get_array(df, "b"))
+
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_squeeze(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]})
+    df_orig = df.copy()
+    series = df.squeeze()
+
+    # Should share memory regardless of CoW since squeeze is just an iloc
+    assert np.shares_memory(series.values, get_array(df, "a"))
+
+    # mutating squeezed df triggers a copy-on-write for that column/block
+    with tm.assert_cow_warning(warn_copy_on_write):
+        series.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(series.values, get_array(df, "a"))
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        # Without CoW the original will be modified
+        assert np.shares_memory(series.values, get_array(df, "a"))
+        assert df.loc[0, "a"] == 0
+
+
+def test_items(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]})
+    df_orig = df.copy()
+
+    # Test this twice, since the second time, the item cache will be
+    # triggered, and we want to make sure it still works then.
+    for i in range(2):
+        for name, ser in df.items():
+            assert np.shares_memory(get_array(ser, name), get_array(df, name))
+
+            # mutating df triggers a copy-on-write for that column / block
+            with tm.assert_cow_warning(warn_copy_on_write):
+                ser.iloc[0] = 0
+
+            if using_copy_on_write:
+                assert not np.shares_memory(get_array(ser, name), get_array(df, name))
+                tm.assert_frame_equal(df, df_orig)
+            else:
+                # Original frame will be modified
+                assert df.loc[0, name] == 0
+
+
+@pytest.mark.parametrize("dtype", ["int64", "Int64"])
+def test_putmask(using_copy_on_write, dtype, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2], "b": 1, "c": 2}, dtype=dtype)
+    view = df[:]
+    df_orig = df.copy()
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df[df == df] = 5
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(view, "a"), get_array(df, "a"))
+        tm.assert_frame_equal(view, df_orig)
+    else:
+        # Without CoW the original will be modified
+        assert np.shares_memory(get_array(view, "a"), get_array(df, "a"))
+        assert view.iloc[0, 0] == 5
+
+
+@pytest.mark.parametrize("dtype", ["int64", "Int64"])
+def test_putmask_no_reference(using_copy_on_write, dtype):
+    df = DataFrame({"a": [1, 2], "b": 1, "c": 2}, dtype=dtype)
+    arr_a = get_array(df, "a")
+    df[df == df] = 5
+
+    if using_copy_on_write:
+        assert np.shares_memory(arr_a, get_array(df, "a"))
+
+
+@pytest.mark.parametrize("dtype", ["float64", "Float64"])
+def test_putmask_aligns_rhs_no_reference(using_copy_on_write, dtype):
+    df = DataFrame({"a": [1.5, 2], "b": 1.5}, dtype=dtype)
+    arr_a = get_array(df, "a")
+    df[df == df] = DataFrame({"a": [5.5, 5]})
+
+    if using_copy_on_write:
+        assert np.shares_memory(arr_a, get_array(df, "a"))
+
+
+@pytest.mark.parametrize(
+    "val, exp, warn", [(5.5, True, FutureWarning), (5, False, None)]
+)
+def test_putmask_dont_copy_some_blocks(
+    using_copy_on_write, val, exp, warn, warn_copy_on_write
+):
+    df = DataFrame({"a": [1, 2], "b": 1, "c": 1.5})
+    view = df[:]
+    df_orig = df.copy()
+    indexer = DataFrame(
+        [[True, False, False], [True, False, False]], columns=list("abc")
+    )
+    if warn_copy_on_write:
+        with tm.assert_cow_warning():
+            df[indexer] = val
+    else:
+        with tm.assert_produces_warning(warn, match="incompatible dtype"):
+            df[indexer] = val
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(view, "a"), get_array(df, "a"))
+        # TODO(CoW): Could split blocks to avoid copying the whole block
+        assert np.shares_memory(get_array(view, "b"), get_array(df, "b")) is exp
+        assert np.shares_memory(get_array(view, "c"), get_array(df, "c"))
+        assert df._mgr._has_no_reference(1) is not exp
+        assert not df._mgr._has_no_reference(2)
+        tm.assert_frame_equal(view, df_orig)
+    elif val == 5:
+        # Without CoW the original will be modified, the other case upcasts, e.g. copy
+        assert np.shares_memory(get_array(view, "a"), get_array(df, "a"))
+        assert np.shares_memory(get_array(view, "c"), get_array(df, "c"))
+        assert view.iloc[0, 0] == 5
+
+
+@pytest.mark.parametrize("dtype", ["int64", "Int64"])
+@pytest.mark.parametrize(
+    "func",
+    [
+        lambda ser: ser.where(ser > 0, 10),
+        lambda ser: ser.mask(ser <= 0, 10),
+    ],
+)
+def test_where_mask_noop(using_copy_on_write, dtype, func):
+    ser = Series([1, 2, 3], dtype=dtype)
+    ser_orig = ser.copy()
+
+    result = func(ser)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(ser), get_array(result))
+    else:
+        assert not np.shares_memory(get_array(ser), get_array(result))
+
+    result.iloc[0] = 10
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(ser), get_array(result))
+    tm.assert_series_equal(ser, ser_orig)
+
+
+@pytest.mark.parametrize("dtype", ["int64", "Int64"])
+@pytest.mark.parametrize(
+    "func",
+    [
+        lambda ser: ser.where(ser < 0, 10),
+        lambda ser: ser.mask(ser >= 0, 10),
+    ],
+)
+def test_where_mask(using_copy_on_write, dtype, func):
+    ser = Series([1, 2, 3], dtype=dtype)
+    ser_orig = ser.copy()
+
+    result = func(ser)
+
+    assert not np.shares_memory(get_array(ser), get_array(result))
+    tm.assert_series_equal(ser, ser_orig)
+
+
+@pytest.mark.parametrize("dtype, val", [("int64", 10.5), ("Int64", 10)])
+@pytest.mark.parametrize(
+    "func",
+    [
+        lambda df, val: df.where(df < 0, val),
+        lambda df, val: df.mask(df >= 0, val),
+    ],
+)
+def test_where_mask_noop_on_single_column(using_copy_on_write, dtype, val, func):
+    df = DataFrame({"a": [1, 2, 3], "b": [-4, -5, -6]}, dtype=dtype)
+    df_orig = df.copy()
+
+    result = func(df, val)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "b"), get_array(result, "b"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+    else:
+        assert not np.shares_memory(get_array(df, "b"), get_array(result, "b"))
+
+    result.iloc[0, 1] = 10
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "b"), get_array(result, "b"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+@pytest.mark.parametrize("func", ["mask", "where"])
+def test_chained_where_mask(using_copy_on_write, func):
+    df = DataFrame({"a": [1, 4, 2], "b": 1})
+    df_orig = df.copy()
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error():
+            getattr(df["a"], func)(df["a"] > 2, 5, inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+
+        with tm.raises_chained_assignment_error():
+            getattr(df[["a"]], func)(df["a"] > 2, 5, inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+            getattr(df["a"], func)(df["a"] > 2, 5, inplace=True)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                getattr(df[["a"]], func)(df["a"] > 2, 5, inplace=True)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                getattr(df[df["a"] > 1], func)(df["a"] > 2, 5, inplace=True)
+
+
+def test_asfreq_noop(using_copy_on_write):
+    df = DataFrame(
+        {"a": [0.0, None, 2.0, 3.0]},
+        index=date_range("1/1/2000", periods=4, freq="min"),
+    )
+    df_orig = df.copy()
+    df2 = df.asfreq(freq="min")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    # mutating df2 triggers a copy-on-write for that column / block
+    df2.iloc[0, 0] = 0
+
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_iterrows(using_copy_on_write):
+    df = DataFrame({"a": 0, "b": 1}, index=[1, 2, 3])
+    df_orig = df.copy()
+
+    for _, sub in df.iterrows():
+        sub.iloc[0] = 100
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+
+
+def test_interpolate_creates_copy(using_copy_on_write, warn_copy_on_write):
+    # GH#51126
+    df = DataFrame({"a": [1.5, np.nan, 3]})
+    view = df[:]
+    expected = df.copy()
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.ffill(inplace=True)
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 100.5
+
+    if using_copy_on_write:
+        tm.assert_frame_equal(view, expected)
+    else:
+        expected = DataFrame({"a": [100.5, 1.5, 3]})
+        tm.assert_frame_equal(view, expected)
+
+
+def test_isetitem(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]})
+    df_orig = df.copy()
+    df2 = df.copy(deep=None)  # Trigger a CoW
+    df2.isetitem(1, np.array([-1, -2, -3]))  # This is inplace
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+        assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+    else:
+        assert not np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    df2.loc[0, "a"] = 0
+    tm.assert_frame_equal(df, df_orig)  # Original is unchanged
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+    else:
+        assert not np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+
+
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+def test_isetitem_series(using_copy_on_write, dtype):
+    df = DataFrame({"a": [1, 2, 3], "b": np.array([4, 5, 6], dtype=dtype)})
+    ser = Series([7, 8, 9])
+    ser_orig = ser.copy()
+    df.isetitem(0, ser)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "a"), get_array(ser))
+        assert not df._mgr._has_no_reference(0)
+
+    # mutating dataframe doesn't update series
+    df.loc[0, "a"] = 0
+    tm.assert_series_equal(ser, ser_orig)
+
+    # mutating series doesn't update dataframe
+    df = DataFrame({"a": [1, 2, 3], "b": np.array([4, 5, 6], dtype=dtype)})
+    ser = Series([7, 8, 9])
+    df.isetitem(0, ser)
+
+    ser.loc[0] = 0
+    expected = DataFrame({"a": [7, 8, 9], "b": np.array([4, 5, 6], dtype=dtype)})
+    tm.assert_frame_equal(df, expected)
+
+
+def test_isetitem_frame(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1, "c": 2})
+    rhs = DataFrame({"a": [4, 5, 6], "b": 2})
+    df.isetitem([0, 1], rhs)
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "a"), get_array(rhs, "a"))
+        assert np.shares_memory(get_array(df, "b"), get_array(rhs, "b"))
+        assert not df._mgr._has_no_reference(0)
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(rhs, "a"))
+        assert not np.shares_memory(get_array(df, "b"), get_array(rhs, "b"))
+    expected = df.copy()
+    rhs.iloc[0, 0] = 100
+    rhs.iloc[0, 1] = 100
+    tm.assert_frame_equal(df, expected)
+
+
+@pytest.mark.parametrize("key", ["a", ["a"]])
+def test_get(using_copy_on_write, warn_copy_on_write, key):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    df_orig = df.copy()
+
+    result = df.get(key)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+        result.iloc[0] = 0
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        # for non-CoW it depends on whether we got a Series or DataFrame if it
+        # is a view or copy or triggers a warning or not
+        if warn_copy_on_write:
+            warn = FutureWarning if isinstance(key, str) else None
+        else:
+            warn = SettingWithCopyWarning if isinstance(key, list) else None
+        with option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(warn):
+                result.iloc[0] = 0
+
+        if isinstance(key, list):
+            tm.assert_frame_equal(df, df_orig)
+        else:
+            assert df.iloc[0, 0] == 0
+
+
+@pytest.mark.parametrize("axis, key", [(0, 0), (1, "a")])
+@pytest.mark.parametrize(
+    "dtype", ["int64", "float64"], ids=["single-block", "mixed-block"]
+)
+def test_xs(
+    using_copy_on_write, warn_copy_on_write, using_array_manager, axis, key, dtype
+):
+    single_block = (dtype == "int64") and not using_array_manager
+    is_view = single_block or (using_array_manager and axis == 1)
+    df = DataFrame(
+        {"a": [1, 2, 3], "b": [4, 5, 6], "c": np.array([7, 8, 9], dtype=dtype)}
+    )
+    df_orig = df.copy()
+
+    result = df.xs(key, axis=axis)
+
+    if axis == 1 or single_block:
+        assert np.shares_memory(get_array(df, "a"), get_array(result))
+    elif using_copy_on_write:
+        assert result._mgr._has_no_reference(0)
+
+    if using_copy_on_write or (is_view and not warn_copy_on_write):
+        result.iloc[0] = 0
+    elif warn_copy_on_write:
+        with tm.assert_cow_warning(single_block or axis == 1):
+            result.iloc[0] = 0
+    else:
+        with option_context("chained_assignment", "warn"):
+            with tm.assert_produces_warning(SettingWithCopyWarning):
+                result.iloc[0] = 0
+
+    if using_copy_on_write or (not single_block and axis == 0):
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert df.iloc[0, 0] == 0
+
+
+@pytest.mark.parametrize("axis", [0, 1])
+@pytest.mark.parametrize("key, level", [("l1", 0), (2, 1)])
+def test_xs_multiindex(
+    using_copy_on_write, warn_copy_on_write, using_array_manager, key, level, axis
+):
+    arr = np.arange(18).reshape(6, 3)
+    index = MultiIndex.from_product([["l1", "l2"], [1, 2, 3]], names=["lev1", "lev2"])
+    df = DataFrame(arr, index=index, columns=list("abc"))
+    if axis == 1:
+        df = df.transpose().copy()
+    df_orig = df.copy()
+
+    result = df.xs(key, level=level, axis=axis)
+
+    if level == 0:
+        assert np.shares_memory(
+            get_array(df, df.columns[0]), get_array(result, result.columns[0])
+        )
+
+    if warn_copy_on_write:
+        warn = FutureWarning if level == 0 else None
+    elif not using_copy_on_write and not using_array_manager:
+        warn = SettingWithCopyWarning
+    else:
+        warn = None
+    with option_context("chained_assignment", "warn"):
+        with tm.assert_produces_warning(warn):
+            result.iloc[0, 0] = 0
+
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_update_frame(using_copy_on_write, warn_copy_on_write):
+    df1 = DataFrame({"a": [1.0, 2.0, 3.0], "b": [4.0, 5.0, 6.0]})
+    df2 = DataFrame({"b": [100.0]}, index=[1])
+    df1_orig = df1.copy()
+    view = df1[:]
+
+    # TODO(CoW) better warning message?
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df1.update(df2)
+
+    expected = DataFrame({"a": [1.0, 2.0, 3.0], "b": [4.0, 100.0, 6.0]})
+    tm.assert_frame_equal(df1, expected)
+    if using_copy_on_write:
+        # df1 is updated, but its view not
+        tm.assert_frame_equal(view, df1_orig)
+        assert np.shares_memory(get_array(df1, "a"), get_array(view, "a"))
+        assert not np.shares_memory(get_array(df1, "b"), get_array(view, "b"))
+    else:
+        tm.assert_frame_equal(view, expected)
+
+
+def test_update_series(using_copy_on_write, warn_copy_on_write):
+    ser1 = Series([1.0, 2.0, 3.0])
+    ser2 = Series([100.0], index=[1])
+    ser1_orig = ser1.copy()
+    view = ser1[:]
+
+    if warn_copy_on_write:
+        with tm.assert_cow_warning():
+            ser1.update(ser2)
+    else:
+        ser1.update(ser2)
+
+    expected = Series([1.0, 100.0, 3.0])
+    tm.assert_series_equal(ser1, expected)
+    if using_copy_on_write:
+        # ser1 is updated, but its view not
+        tm.assert_series_equal(view, ser1_orig)
+    else:
+        tm.assert_series_equal(view, expected)
+
+
+def test_update_chained_assignment(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]})
+    ser2 = Series([100.0], index=[1])
+    df_orig = df.copy()
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error():
+            df["a"].update(ser2)
+        tm.assert_frame_equal(df, df_orig)
+
+        with tm.raises_chained_assignment_error():
+            df[["a"]].update(ser2.to_frame())
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+            df["a"].update(ser2)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                df[["a"]].update(ser2.to_frame())
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                df[df["a"] > 1].update(ser2.to_frame())
+
+
+def test_inplace_arithmetic_series(using_copy_on_write):
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+    data = get_array(ser)
+    ser *= 2
+    if using_copy_on_write:
+        # https://github.com/pandas-dev/pandas/pull/55745
+        # changed to NOT update inplace because there is no benefit (actual
+        # operation already done non-inplace). This was only for the optics
+        # of updating the backing array inplace, but we no longer want to make
+        # that guarantee
+        assert not np.shares_memory(get_array(ser), data)
+        tm.assert_numpy_array_equal(data, get_array(ser_orig))
+    else:
+        assert np.shares_memory(get_array(ser), data)
+        tm.assert_numpy_array_equal(data, get_array(ser))
+
+
+def test_inplace_arithmetic_series_with_reference(
+    using_copy_on_write, warn_copy_on_write
+):
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+    view = ser[:]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser *= 2
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(ser), get_array(view))
+        tm.assert_series_equal(ser_orig, view)
+    else:
+        assert np.shares_memory(get_array(ser), get_array(view))
+
+
+@pytest.mark.parametrize("copy", [True, False])
+def test_transpose(using_copy_on_write, copy, using_array_manager):
+    df = DataFrame({"a": [1, 2, 3], "b": 1})
+    df_orig = df.copy()
+    result = df.transpose(copy=copy)
+
+    if not copy and not using_array_manager or using_copy_on_write:
+        assert np.shares_memory(get_array(df, "a"), get_array(result, 0))
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, 0))
+
+    result.iloc[0, 0] = 100
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+
+
+def test_transpose_different_dtypes(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1.5})
+    df_orig = df.copy()
+    result = df.T
+
+    assert not np.shares_memory(get_array(df, "a"), get_array(result, 0))
+    result.iloc[0, 0] = 100
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+
+
+def test_transpose_ea_single_column(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]}, dtype="Int64")
+    result = df.T
+
+    assert not np.shares_memory(get_array(df, "a"), get_array(result, 0))
+
+
+def test_transform_frame(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1})
+    df_orig = df.copy()
+
+    def func(ser):
+        ser.iloc[0] = 100
+        return ser
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.transform(func)
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+
+
+def test_transform_series(using_copy_on_write, warn_copy_on_write):
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+
+    def func(ser):
+        ser.iloc[0] = 100
+        return ser
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser.transform(func)
+    if using_copy_on_write:
+        tm.assert_series_equal(ser, ser_orig)
+
+
+def test_count_read_only_array():
+    df = DataFrame({"a": [1, 2], "b": 3})
+    result = df.count()
+    result.iloc[0] = 100
+    expected = Series([100, 2], index=["a", "b"])
+    tm.assert_series_equal(result, expected)
+
+
+def test_series_view(using_copy_on_write, warn_copy_on_write):
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+
+    with tm.assert_produces_warning(FutureWarning, match="is deprecated"):
+        ser2 = ser.view()
+    assert np.shares_memory(get_array(ser), get_array(ser2))
+    if using_copy_on_write:
+        assert not ser2._mgr._has_no_reference(0)
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser2.iloc[0] = 100
+
+    if using_copy_on_write:
+        tm.assert_series_equal(ser_orig, ser)
+    else:
+        expected = Series([100, 2, 3])
+        tm.assert_series_equal(ser, expected)
+
+
+def test_insert_series(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]})
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+    df.insert(loc=1, value=ser, column="b")
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(ser), get_array(df, "b"))
+        assert not df._mgr._has_no_reference(1)
+    else:
+        assert not np.shares_memory(get_array(ser), get_array(df, "b"))
+
+    df.iloc[0, 1] = 100
+    tm.assert_series_equal(ser, ser_orig)
+
+
+def test_eval(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1})
+    df_orig = df.copy()
+
+    result = df.eval("c = a+b")
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+
+    result.iloc[0, 0] = 100
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_eval_inplace(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": 1})
+    df_orig = df.copy()
+    df_view = df[:]
+
+    df.eval("c = a+b", inplace=True)
+    assert np.shares_memory(get_array(df, "a"), get_array(df_view, "a"))
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.iloc[0, 0] = 100
+    if using_copy_on_write:
+        tm.assert_frame_equal(df_view, df_orig)
+
+
+def test_apply_modify_row(using_copy_on_write, warn_copy_on_write):
+    # Case: applying a function on each row as a Series object, where the
+    # function mutates the row object (which needs to trigger CoW if row is a view)
+    df = DataFrame({"A": [1, 2], "B": [3, 4]})
+    df_orig = df.copy()
+
+    def transform(row):
+        row["B"] = 100
+        return row
+
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.apply(transform, axis=1)
+
+    if using_copy_on_write:
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        assert df.loc[0, "B"] == 100
+
+    # row Series is a copy
+    df = DataFrame({"A": [1, 2], "B": ["b", "c"]})
+    df_orig = df.copy()
+
+    with tm.assert_produces_warning(None):
+        df.apply(transform, axis=1)
+
+    tm.assert_frame_equal(df, df_orig)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_replace.py

@@ -0,0 +1,481 @@
+import numpy as np
+import pytest
+
+from pandas import (
+    Categorical,
+    DataFrame,
+    option_context,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+
+@pytest.mark.parametrize(
+    "replace_kwargs",
+    [
+        {"to_replace": {"a": 1, "b": 4}, "value": -1},
+        # Test CoW splits blocks to avoid copying unchanged columns
+        {"to_replace": {"a": 1}, "value": -1},
+        {"to_replace": {"b": 4}, "value": -1},
+        {"to_replace": {"b": {4: 1}}},
+        # TODO: Add these in a further optimization
+        # We would need to see which columns got replaced in the mask
+        # which could be expensive
+        # {"to_replace": {"b": 1}},
+        # 1
+    ],
+)
+def test_replace(using_copy_on_write, replace_kwargs):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": ["foo", "bar", "baz"]})
+    df_orig = df.copy()
+
+    df_replaced = df.replace(**replace_kwargs)
+
+    if using_copy_on_write:
+        if (df_replaced["b"] == df["b"]).all():
+            assert np.shares_memory(get_array(df_replaced, "b"), get_array(df, "b"))
+        assert np.shares_memory(get_array(df_replaced, "c"), get_array(df, "c"))
+
+    # mutating squeezed df triggers a copy-on-write for that column/block
+    df_replaced.loc[0, "c"] = -1
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df_replaced, "c"), get_array(df, "c"))
+
+    if "a" in replace_kwargs["to_replace"]:
+        arr = get_array(df_replaced, "a")
+        df_replaced.loc[0, "a"] = 100
+        assert np.shares_memory(get_array(df_replaced, "a"), arr)
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_replace_regex_inplace_refs(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": ["aaa", "bbb"]})
+    df_orig = df.copy()
+    view = df[:]
+    arr = get_array(df, "a")
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.replace(to_replace=r"^a.*$", value="new", inplace=True, regex=True)
+    if using_copy_on_write:
+        assert not np.shares_memory(arr, get_array(df, "a"))
+        assert df._mgr._has_no_reference(0)
+        tm.assert_frame_equal(view, df_orig)
+    else:
+        assert np.shares_memory(arr, get_array(df, "a"))
+
+
+def test_replace_regex_inplace(using_copy_on_write):
+    df = DataFrame({"a": ["aaa", "bbb"]})
+    arr = get_array(df, "a")
+    df.replace(to_replace=r"^a.*$", value="new", inplace=True, regex=True)
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+    assert np.shares_memory(arr, get_array(df, "a"))
+
+    df_orig = df.copy()
+    df2 = df.replace(to_replace=r"^b.*$", value="new", regex=True)
+    tm.assert_frame_equal(df_orig, df)
+    assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+
+def test_replace_regex_inplace_no_op(using_copy_on_write):
+    df = DataFrame({"a": [1, 2]})
+    arr = get_array(df, "a")
+    df.replace(to_replace=r"^a.$", value="new", inplace=True, regex=True)
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+    assert np.shares_memory(arr, get_array(df, "a"))
+
+    df_orig = df.copy()
+    df2 = df.replace(to_replace=r"^x.$", value="new", regex=True)
+    tm.assert_frame_equal(df_orig, df)
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+
+def test_replace_mask_all_false_second_block(using_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3], "b": 100.5, "c": 1, "d": 2})
+    df_orig = df.copy()
+
+    df2 = df.replace(to_replace=1.5, value=55.5)
+
+    if using_copy_on_write:
+        # TODO: Block splitting would allow us to avoid copying b
+        assert np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    else:
+        assert not np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    df2.loc[0, "c"] = 1
+    tm.assert_frame_equal(df, df_orig)  # Original is unchanged
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+        # TODO: This should split and not copy the whole block
+        # assert np.shares_memory(get_array(df, "d"), get_array(df2, "d"))
+
+
+def test_replace_coerce_single_column(using_copy_on_write, using_array_manager):
+    df = DataFrame({"a": [1.5, 2, 3], "b": 100.5})
+    df_orig = df.copy()
+
+    df2 = df.replace(to_replace=1.5, value="a")
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    elif not using_array_manager:
+        assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    if using_copy_on_write:
+        df2.loc[0, "b"] = 0.5
+        tm.assert_frame_equal(df, df_orig)  # Original is unchanged
+        assert not np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+
+
+def test_replace_to_replace_wrong_dtype(using_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3], "b": 100.5})
+    df_orig = df.copy()
+
+    df2 = df.replace(to_replace="xxx", value=1.5)
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+        assert np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    else:
+        assert not np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+        assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+    df2.loc[0, "b"] = 0.5
+    tm.assert_frame_equal(df, df_orig)  # Original is unchanged
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "b"), get_array(df2, "b"))
+
+
+def test_replace_list_categorical(using_copy_on_write):
+    df = DataFrame({"a": ["a", "b", "c"]}, dtype="category")
+    arr = get_array(df, "a")
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.replace(["c"], value="a", inplace=True)
+    assert np.shares_memory(arr.codes, get_array(df, "a").codes)
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+
+    df_orig = df.copy()
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df2 = df.replace(["b"], value="a")
+    assert not np.shares_memory(arr.codes, get_array(df2, "a").codes)
+
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_replace_list_inplace_refs_categorical(using_copy_on_write):
+    df = DataFrame({"a": ["a", "b", "c"]}, dtype="category")
+    view = df[:]
+    df_orig = df.copy()
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.replace(["c"], value="a", inplace=True)
+    if using_copy_on_write:
+        assert not np.shares_memory(
+            get_array(view, "a").codes, get_array(df, "a").codes
+        )
+        tm.assert_frame_equal(df_orig, view)
+    else:
+        # This could be inplace
+        assert not np.shares_memory(
+            get_array(view, "a").codes, get_array(df, "a").codes
+        )
+
+
+@pytest.mark.parametrize("to_replace", [1.5, [1.5], []])
+def test_replace_inplace(using_copy_on_write, to_replace):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    arr_a = get_array(df, "a")
+    df.replace(to_replace=1.5, value=15.5, inplace=True)
+
+    assert np.shares_memory(get_array(df, "a"), arr_a)
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+
+
+@pytest.mark.parametrize("to_replace", [1.5, [1.5]])
+def test_replace_inplace_reference(using_copy_on_write, to_replace, warn_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    arr_a = get_array(df, "a")
+    view = df[:]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.replace(to_replace=to_replace, value=15.5, inplace=True)
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), arr_a)
+        assert df._mgr._has_no_reference(0)
+        assert view._mgr._has_no_reference(0)
+    else:
+        assert np.shares_memory(get_array(df, "a"), arr_a)
+
+
+@pytest.mark.parametrize("to_replace", ["a", 100.5])
+def test_replace_inplace_reference_no_op(using_copy_on_write, to_replace):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    arr_a = get_array(df, "a")
+    view = df[:]
+    df.replace(to_replace=to_replace, value=15.5, inplace=True)
+
+    assert np.shares_memory(get_array(df, "a"), arr_a)
+    if using_copy_on_write:
+        assert not df._mgr._has_no_reference(0)
+        assert not view._mgr._has_no_reference(0)
+
+
+@pytest.mark.parametrize("to_replace", [1, [1]])
+@pytest.mark.parametrize("val", [1, 1.5])
+def test_replace_categorical_inplace_reference(using_copy_on_write, val, to_replace):
+    df = DataFrame({"a": Categorical([1, 2, 3])})
+    df_orig = df.copy()
+    arr_a = get_array(df, "a")
+    view = df[:]
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    warn = FutureWarning if val == 1.5 else None
+    with tm.assert_produces_warning(warn, match=msg):
+        df.replace(to_replace=to_replace, value=val, inplace=True)
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a").codes, arr_a.codes)
+        assert df._mgr._has_no_reference(0)
+        assert view._mgr._has_no_reference(0)
+        tm.assert_frame_equal(view, df_orig)
+    else:
+        assert np.shares_memory(get_array(df, "a").codes, arr_a.codes)
+
+
+@pytest.mark.parametrize("val", [1, 1.5])
+def test_replace_categorical_inplace(using_copy_on_write, val):
+    df = DataFrame({"a": Categorical([1, 2, 3])})
+    arr_a = get_array(df, "a")
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    warn = FutureWarning if val == 1.5 else None
+    with tm.assert_produces_warning(warn, match=msg):
+        df.replace(to_replace=1, value=val, inplace=True)
+
+    assert np.shares_memory(get_array(df, "a").codes, arr_a.codes)
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+
+    expected = DataFrame({"a": Categorical([val, 2, 3])})
+    tm.assert_frame_equal(df, expected)
+
+
+@pytest.mark.parametrize("val", [1, 1.5])
+def test_replace_categorical(using_copy_on_write, val):
+    df = DataFrame({"a": Categorical([1, 2, 3])})
+    df_orig = df.copy()
+    msg = (
+        r"The behavior of Series\.replace \(and DataFrame.replace\) "
+        "with CategoricalDtype"
+    )
+    warn = FutureWarning if val == 1.5 else None
+    with tm.assert_produces_warning(warn, match=msg):
+        df2 = df.replace(to_replace=1, value=val)
+
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+        assert df2._mgr._has_no_reference(0)
+    assert not np.shares_memory(get_array(df, "a").codes, get_array(df2, "a").codes)
+    tm.assert_frame_equal(df, df_orig)
+
+    arr_a = get_array(df2, "a").codes
+    df2.iloc[0, 0] = 2.0
+    assert np.shares_memory(get_array(df2, "a").codes, arr_a)
+
+
+@pytest.mark.parametrize("method", ["where", "mask"])
+def test_masking_inplace(using_copy_on_write, method, warn_copy_on_write):
+    df = DataFrame({"a": [1.5, 2, 3]})
+    df_orig = df.copy()
+    arr_a = get_array(df, "a")
+    view = df[:]
+
+    method = getattr(df, method)
+    if warn_copy_on_write:
+        with tm.assert_cow_warning():
+            method(df["a"] > 1.6, -1, inplace=True)
+    else:
+        method(df["a"] > 1.6, -1, inplace=True)
+
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), arr_a)
+        assert df._mgr._has_no_reference(0)
+        assert view._mgr._has_no_reference(0)
+        tm.assert_frame_equal(view, df_orig)
+    else:
+        assert np.shares_memory(get_array(df, "a"), arr_a)
+
+
+def test_replace_empty_list(using_copy_on_write):
+    df = DataFrame({"a": [1, 2]})
+
+    df2 = df.replace([], [])
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+        assert not df._mgr._has_no_reference(0)
+    else:
+        assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+
+    arr_a = get_array(df, "a")
+    df.replace([], [])
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "a"), arr_a)
+        assert not df._mgr._has_no_reference(0)
+        assert not df2._mgr._has_no_reference(0)
+
+
+@pytest.mark.parametrize("value", ["d", None])
+def test_replace_object_list_inplace(using_copy_on_write, value):
+    df = DataFrame({"a": ["a", "b", "c"]})
+    arr = get_array(df, "a")
+    df.replace(["c"], value, inplace=True)
+    if using_copy_on_write or value is None:
+        assert np.shares_memory(arr, get_array(df, "a"))
+    else:
+        # This could be inplace
+        assert not np.shares_memory(arr, get_array(df, "a"))
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+
+
+def test_replace_list_multiple_elements_inplace(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3]})
+    arr = get_array(df, "a")
+    df.replace([1, 2], 4, inplace=True)
+    if using_copy_on_write:
+        assert np.shares_memory(arr, get_array(df, "a"))
+        assert df._mgr._has_no_reference(0)
+    else:
+        assert np.shares_memory(arr, get_array(df, "a"))
+
+
+def test_replace_list_none(using_copy_on_write):
+    df = DataFrame({"a": ["a", "b", "c"]})
+
+    df_orig = df.copy()
+    df2 = df.replace(["b"], value=None)
+    tm.assert_frame_equal(df, df_orig)
+
+    assert not np.shares_memory(get_array(df, "a"), get_array(df2, "a"))
+
+
+def test_replace_list_none_inplace_refs(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": ["a", "b", "c"]})
+    arr = get_array(df, "a")
+    df_orig = df.copy()
+    view = df[:]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.replace(["a"], value=None, inplace=True)
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+        assert not np.shares_memory(arr, get_array(df, "a"))
+        tm.assert_frame_equal(df_orig, view)
+    else:
+        assert np.shares_memory(arr, get_array(df, "a"))
+
+
+def test_replace_columnwise_no_op_inplace(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [1, 2, 3]})
+    view = df[:]
+    df_orig = df.copy()
+    df.replace({"a": 10}, 100, inplace=True)
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(view, "a"), get_array(df, "a"))
+        df.iloc[0, 0] = 100
+        tm.assert_frame_equal(view, df_orig)
+
+
+def test_replace_columnwise_no_op(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [1, 2, 3]})
+    df_orig = df.copy()
+    df2 = df.replace({"a": 10}, 100)
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
+    df2.iloc[0, 0] = 100
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_replace_chained_assignment(using_copy_on_write):
+    df = DataFrame({"a": [1, np.nan, 2], "b": 1})
+    df_orig = df.copy()
+    if using_copy_on_write:
+        with tm.raises_chained_assignment_error():
+            df["a"].replace(1, 100, inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+
+        with tm.raises_chained_assignment_error():
+            df[["a"]].replace(1, 100, inplace=True)
+        tm.assert_frame_equal(df, df_orig)
+    else:
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                df[["a"]].replace(1, 100, inplace=True)
+
+        with tm.assert_produces_warning(None):
+            with option_context("mode.chained_assignment", None):
+                df[df.a > 5].replace(1, 100, inplace=True)
+
+        with tm.assert_produces_warning(FutureWarning, match="inplace method"):
+            df["a"].replace(1, 100, inplace=True)
+
+
+def test_replace_listlike(using_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [1, 2, 3]})
+    df_orig = df.copy()
+
+    result = df.replace([200, 201], [11, 11])
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+    else:
+        assert not np.shares_memory(get_array(result, "a"), get_array(df, "a"))
+
+    result.iloc[0, 0] = 100
+    tm.assert_frame_equal(df, df)
+
+    result = df.replace([200, 2], [10, 10])
+    assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+    tm.assert_frame_equal(df, df_orig)
+
+
+def test_replace_listlike_inplace(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [1, 2, 3]})
+    arr = get_array(df, "a")
+    df.replace([200, 2], [10, 11], inplace=True)
+    assert np.shares_memory(get_array(df, "a"), arr)
+
+    view = df[:]
+    df_orig = df.copy()
+    with tm.assert_cow_warning(warn_copy_on_write):
+        df.replace([200, 3], [10, 11], inplace=True)
+    if using_copy_on_write:
+        assert not np.shares_memory(get_array(df, "a"), arr)
+        tm.assert_frame_equal(view, df_orig)
+    else:
+        assert np.shares_memory(get_array(df, "a"), arr)
+        tm.assert_frame_equal(df, view)

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_setitem.py

@@ -0,0 +1,156 @@
+import numpy as np
+
+from pandas import (
+    DataFrame,
+    Index,
+    MultiIndex,
+    RangeIndex,
+    Series,
+)
+import pandas._testing as tm
+from pandas.tests.copy_view.util import get_array
+
+# -----------------------------------------------------------------------------
+# Copy/view behaviour for the values that are set in a DataFrame
+
+
+def test_set_column_with_array():
+    # Case: setting an array as a new column (df[col] = arr) copies that data
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    arr = np.array([1, 2, 3], dtype="int64")
+
+    df["c"] = arr
+
+    # the array data is copied
+    assert not np.shares_memory(get_array(df, "c"), arr)
+    # and thus modifying the array does not modify the DataFrame
+    arr[0] = 0
+    tm.assert_series_equal(df["c"], Series([1, 2, 3], name="c"))
+
+
+def test_set_column_with_series(using_copy_on_write):
+    # Case: setting a series as a new column (df[col] = s) copies that data
+    # (with delayed copy with CoW)
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    ser = Series([1, 2, 3])
+
+    df["c"] = ser
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "c"), get_array(ser))
+    else:
+        # the series data is copied
+        assert not np.shares_memory(get_array(df, "c"), get_array(ser))
+
+    # and modifying the series does not modify the DataFrame
+    ser.iloc[0] = 0
+    assert ser.iloc[0] == 0
+    tm.assert_series_equal(df["c"], Series([1, 2, 3], name="c"))
+
+
+def test_set_column_with_index(using_copy_on_write):
+    # Case: setting an index as a new column (df[col] = idx) copies that data
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    idx = Index([1, 2, 3])
+
+    df["c"] = idx
+
+    # the index data is copied
+    assert not np.shares_memory(get_array(df, "c"), idx.values)
+
+    idx = RangeIndex(1, 4)
+    arr = idx.values
+
+    df["d"] = idx
+
+    assert not np.shares_memory(get_array(df, "d"), arr)
+
+
+def test_set_columns_with_dataframe(using_copy_on_write):
+    # Case: setting a DataFrame as new columns copies that data
+    # (with delayed copy with CoW)
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    df2 = DataFrame({"c": [7, 8, 9], "d": [10, 11, 12]})
+
+    df[["c", "d"]] = df2
+
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+    else:
+        # the data is copied
+        assert not np.shares_memory(get_array(df, "c"), get_array(df2, "c"))
+
+    # and modifying the set DataFrame does not modify the original DataFrame
+    df2.iloc[0, 0] = 0
+    tm.assert_series_equal(df["c"], Series([7, 8, 9], name="c"))
+
+
+def test_setitem_series_no_copy(using_copy_on_write):
+    # Case: setting a Series as column into a DataFrame can delay copying that data
+    df = DataFrame({"a": [1, 2, 3]})
+    rhs = Series([4, 5, 6])
+    rhs_orig = rhs.copy()
+
+    # adding a new column
+    df["b"] = rhs
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(rhs), get_array(df, "b"))
+
+    df.iloc[0, 1] = 100
+    tm.assert_series_equal(rhs, rhs_orig)
+
+
+def test_setitem_series_no_copy_single_block(using_copy_on_write):
+    # Overwriting an existing column that is a single block
+    df = DataFrame({"a": [1, 2, 3], "b": [0.1, 0.2, 0.3]})
+    rhs = Series([4, 5, 6])
+    rhs_orig = rhs.copy()
+
+    df["a"] = rhs
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(rhs), get_array(df, "a"))
+
+    df.iloc[0, 0] = 100
+    tm.assert_series_equal(rhs, rhs_orig)
+
+
+def test_setitem_series_no_copy_split_block(using_copy_on_write):
+    # Overwriting an existing column that is part of a larger block
+    df = DataFrame({"a": [1, 2, 3], "b": 1})
+    rhs = Series([4, 5, 6])
+    rhs_orig = rhs.copy()
+
+    df["b"] = rhs
+    if using_copy_on_write:
+        assert np.shares_memory(get_array(rhs), get_array(df, "b"))
+
+    df.iloc[0, 1] = 100
+    tm.assert_series_equal(rhs, rhs_orig)
+
+
+def test_setitem_series_column_midx_broadcasting(using_copy_on_write):
+    # Setting a Series to multiple columns will repeat the data
+    # (currently copying the data eagerly)
+    df = DataFrame(
+        [[1, 2, 3], [3, 4, 5]],
+        columns=MultiIndex.from_arrays([["a", "a", "b"], [1, 2, 3]]),
+    )
+    rhs = Series([10, 11])
+    df["a"] = rhs
+    assert not np.shares_memory(get_array(rhs), df._get_column_array(0))
+    if using_copy_on_write:
+        assert df._mgr._has_no_reference(0)
+
+
+def test_set_column_with_inplace_operator(using_copy_on_write, warn_copy_on_write):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+
+    # this should not raise any warning
+    with tm.assert_produces_warning(None):
+        df["a"] += 1
+
+    # when it is not in a chain, then it should produce a warning
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    ser = df["a"]
+    with tm.assert_cow_warning(warn_copy_on_write):
+        ser += 1

valley/lib/python3.10/site-packages/pandas/tests/copy_view/test_util.py

@@ -0,0 +1,14 @@
+import numpy as np
+
+from pandas import DataFrame
+from pandas.tests.copy_view.util import get_array
+
+
+def test_get_array_numpy():
+    df = DataFrame({"a": [1, 2, 3]})
+    assert np.shares_memory(get_array(df, "a"), get_array(df, "a"))
+
+
+def test_get_array_masked():
+    df = DataFrame({"a": [1, 2, 3]}, dtype="Int64")
+    assert np.shares_memory(get_array(df, "a"), get_array(df, "a"))

valley/lib/python3.10/site-packages/pandas/tests/copy_view/util.py

@@ -0,0 +1,30 @@
+from pandas import (
+    Categorical,
+    Index,
+    Series,
+)
+from pandas.core.arrays import BaseMaskedArray
+
+
+def get_array(obj, col=None):
+    """
+    Helper method to get array for a DataFrame column or a Series.
+
+    Equivalent of df[col].values, but without going through normal getitem,
+    which triggers tracking references / CoW (and we might be testing that
+    this is done by some other operation).
+    """
+    if isinstance(obj, Index):
+        arr = obj._values
+    elif isinstance(obj, Series) and (col is None or obj.name == col):
+        arr = obj._values
+    else:
+        assert col is not None
+        icol = obj.columns.get_loc(col)
+        assert isinstance(icol, int)
+        arr = obj._get_column_array(icol)
+    if isinstance(arr, BaseMaskedArray):
+        return arr._data
+    elif isinstance(arr, Categorical):
+        return arr
+    return getattr(arr, "_ndarray", arr)

valley/lib/python3.10/site-packages/pandas/tests/interchange/test_impl.py

@@ -0,0 +1,604 @@
+from datetime import (
+    datetime,
+    timezone,
+)
+
+import numpy as np
+import pytest
+
+from pandas._libs.tslibs import iNaT
+from pandas.compat import (
+    is_ci_environment,
+    is_platform_windows,
+)
+from pandas.compat.numpy import np_version_lt1p23
+
+import pandas as pd
+import pandas._testing as tm
+from pandas.core.interchange.column import PandasColumn
+from pandas.core.interchange.dataframe_protocol import (
+    ColumnNullType,
+    DtypeKind,
+)
+from pandas.core.interchange.from_dataframe import from_dataframe
+from pandas.core.interchange.utils import ArrowCTypes
+
+
+@pytest.fixture
+def data_categorical():
+    return {
+        "ordered": pd.Categorical(list("testdata") * 30, ordered=True),
+        "unordered": pd.Categorical(list("testdata") * 30, ordered=False),
+    }
+
+
+@pytest.fixture
+def string_data():
+    return {
+        "separator data": [
+            "abC|DeF,Hik",
+            "234,3245.67",
+            "gSaf,qWer|Gre",
+            "asd3,4sad|",
+            np.nan,
+        ]
+    }
+
+
+@pytest.mark.parametrize("data", [("ordered", True), ("unordered", False)])
+def test_categorical_dtype(data, data_categorical):
+    df = pd.DataFrame({"A": (data_categorical[data[0]])})
+
+    col = df.__dataframe__().get_column_by_name("A")
+    assert col.dtype[0] == DtypeKind.CATEGORICAL
+    assert col.null_count == 0
+    assert col.describe_null == (ColumnNullType.USE_SENTINEL, -1)
+    assert col.num_chunks() == 1
+    desc_cat = col.describe_categorical
+    assert desc_cat["is_ordered"] == data[1]
+    assert desc_cat["is_dictionary"] is True
+    assert isinstance(desc_cat["categories"], PandasColumn)
+    tm.assert_series_equal(
+        desc_cat["categories"]._col, pd.Series(["a", "d", "e", "s", "t"])
+    )
+
+    tm.assert_frame_equal(df, from_dataframe(df.__dataframe__()))
+
+
+def test_categorical_pyarrow():
+    # GH 49889
+    pa = pytest.importorskip("pyarrow", "11.0.0")
+
+    arr = ["Mon", "Tue", "Mon", "Wed", "Mon", "Thu", "Fri", "Sat", "Sun"]
+    table = pa.table({"weekday": pa.array(arr).dictionary_encode()})
+    exchange_df = table.__dataframe__()
+    result = from_dataframe(exchange_df)
+    weekday = pd.Categorical(
+        arr, categories=["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
+    )
+    expected = pd.DataFrame({"weekday": weekday})
+    tm.assert_frame_equal(result, expected)
+
+
+def test_empty_categorical_pyarrow():
+    # https://github.com/pandas-dev/pandas/issues/53077
+    pa = pytest.importorskip("pyarrow", "11.0.0")
+
+    arr = [None]
+    table = pa.table({"arr": pa.array(arr, "float64").dictionary_encode()})
+    exchange_df = table.__dataframe__()
+    result = pd.api.interchange.from_dataframe(exchange_df)
+    expected = pd.DataFrame({"arr": pd.Categorical([np.nan])})
+    tm.assert_frame_equal(result, expected)
+
+
+def test_large_string_pyarrow():
+    # GH 52795
+    pa = pytest.importorskip("pyarrow", "11.0.0")
+
+    arr = ["Mon", "Tue"]
+    table = pa.table({"weekday": pa.array(arr, "large_string")})
+    exchange_df = table.__dataframe__()
+    result = from_dataframe(exchange_df)
+    expected = pd.DataFrame({"weekday": ["Mon", "Tue"]})
+    tm.assert_frame_equal(result, expected)
+
+    # check round-trip
+    assert pa.Table.equals(pa.interchange.from_dataframe(result), table)
+
+
+@pytest.mark.parametrize(
+    ("offset", "length", "expected_values"),
+    [
+        (0, None, [3.3, float("nan"), 2.1]),
+        (1, None, [float("nan"), 2.1]),
+        (2, None, [2.1]),
+        (0, 2, [3.3, float("nan")]),
+        (0, 1, [3.3]),
+        (1, 1, [float("nan")]),
+    ],
+)
+def test_bitmasks_pyarrow(offset, length, expected_values):
+    # GH 52795
+    pa = pytest.importorskip("pyarrow", "11.0.0")
+
+    arr = [3.3, None, 2.1]
+    table = pa.table({"arr": arr}).slice(offset, length)
+    exchange_df = table.__dataframe__()
+    result = from_dataframe(exchange_df)
+    expected = pd.DataFrame({"arr": expected_values})
+    tm.assert_frame_equal(result, expected)
+
+    # check round-trip
+    assert pa.Table.equals(pa.interchange.from_dataframe(result), table)
+
+
+@pytest.mark.parametrize(
+    "data",
+    [
+        lambda: np.random.default_rng(2).integers(-100, 100),
+        lambda: np.random.default_rng(2).integers(1, 100),
+        lambda: np.random.default_rng(2).random(),
+        lambda: np.random.default_rng(2).choice([True, False]),
+        lambda: datetime(
+            year=np.random.default_rng(2).integers(1900, 2100),
+            month=np.random.default_rng(2).integers(1, 12),
+            day=np.random.default_rng(2).integers(1, 20),
+        ),
+    ],
+)
+def test_dataframe(data):
+    NCOLS, NROWS = 10, 20
+    data = {
+        f"col{int((i - NCOLS / 2) % NCOLS + 1)}": [data() for _ in range(NROWS)]
+        for i in range(NCOLS)
+    }
+    df = pd.DataFrame(data)
+
+    df2 = df.__dataframe__()
+
+    assert df2.num_columns() == NCOLS
+    assert df2.num_rows() == NROWS
+
+    assert list(df2.column_names()) == list(data.keys())
+
+    indices = (0, 2)
+    names = tuple(list(data.keys())[idx] for idx in indices)
+
+    result = from_dataframe(df2.select_columns(indices))
+    expected = from_dataframe(df2.select_columns_by_name(names))
+    tm.assert_frame_equal(result, expected)
+
+    assert isinstance(result.attrs["_INTERCHANGE_PROTOCOL_BUFFERS"], list)
+    assert isinstance(expected.attrs["_INTERCHANGE_PROTOCOL_BUFFERS"], list)
+
+
+def test_missing_from_masked():
+    df = pd.DataFrame(
+        {
+            "x": np.array([1.0, 2.0, 3.0, 4.0, 0.0]),
+            "y": np.array([1.5, 2.5, 3.5, 4.5, 0]),
+            "z": np.array([1.0, 0.0, 1.0, 1.0, 1.0]),
+        }
+    )
+
+    rng = np.random.default_rng(2)
+    dict_null = {col: rng.integers(low=0, high=len(df)) for col in df.columns}
+    for col, num_nulls in dict_null.items():
+        null_idx = df.index[
+            rng.choice(np.arange(len(df)), size=num_nulls, replace=False)
+        ]
+        df.loc[null_idx, col] = None
+
+    df2 = df.__dataframe__()
+
+    assert df2.get_column_by_name("x").null_count == dict_null["x"]
+    assert df2.get_column_by_name("y").null_count == dict_null["y"]
+    assert df2.get_column_by_name("z").null_count == dict_null["z"]
+
+
+@pytest.mark.parametrize(
+    "data",
+    [
+        {"x": [1.5, 2.5, 3.5], "y": [9.2, 10.5, 11.8]},
+        {"x": [1, 2, 0], "y": [9.2, 10.5, 11.8]},
+        {
+            "x": np.array([True, True, False]),
+            "y": np.array([1, 2, 0]),
+            "z": np.array([9.2, 10.5, 11.8]),
+        },
+    ],
+)
+def test_mixed_data(data):
+    df = pd.DataFrame(data)
+    df2 = df.__dataframe__()
+
+    for col_name in df.columns:
+        assert df2.get_column_by_name(col_name).null_count == 0
+
+
+def test_mixed_missing():
+    df = pd.DataFrame(
+        {
+            "x": np.array([True, None, False, None, True]),
+            "y": np.array([None, 2, None, 1, 2]),
+            "z": np.array([9.2, 10.5, None, 11.8, None]),
+        }
+    )
+
+    df2 = df.__dataframe__()
+
+    for col_name in df.columns:
+        assert df2.get_column_by_name(col_name).null_count == 2
+
+
+def test_string(string_data):
+    test_str_data = string_data["separator data"] + [""]
+    df = pd.DataFrame({"A": test_str_data})
+    col = df.__dataframe__().get_column_by_name("A")
+
+    assert col.size() == 6
+    assert col.null_count == 1
+    assert col.dtype[0] == DtypeKind.STRING
+    assert col.describe_null == (ColumnNullType.USE_BYTEMASK, 0)
+
+    df_sliced = df[1:]
+    col = df_sliced.__dataframe__().get_column_by_name("A")
+    assert col.size() == 5
+    assert col.null_count == 1
+    assert col.dtype[0] == DtypeKind.STRING
+    assert col.describe_null == (ColumnNullType.USE_BYTEMASK, 0)
+
+
+def test_nonstring_object():
+    df = pd.DataFrame({"A": ["a", 10, 1.0, ()]})
+    col = df.__dataframe__().get_column_by_name("A")
+    with pytest.raises(NotImplementedError, match="not supported yet"):
+        col.dtype
+
+
+def test_datetime():
+    df = pd.DataFrame({"A": [pd.Timestamp("2022-01-01"), pd.NaT]})
+    col = df.__dataframe__().get_column_by_name("A")
+
+    assert col.size() == 2
+    assert col.null_count == 1
+    assert col.dtype[0] == DtypeKind.DATETIME
+    assert col.describe_null == (ColumnNullType.USE_SENTINEL, iNaT)
+
+    tm.assert_frame_equal(df, from_dataframe(df.__dataframe__()))
+
+
+@pytest.mark.skipif(np_version_lt1p23, reason="Numpy > 1.23 required")
+def test_categorical_to_numpy_dlpack():
+    # https://github.com/pandas-dev/pandas/issues/48393
+    df = pd.DataFrame({"A": pd.Categorical(["a", "b", "a"])})
+    col = df.__dataframe__().get_column_by_name("A")
+    result = np.from_dlpack(col.get_buffers()["data"][0])
+    expected = np.array([0, 1, 0], dtype="int8")
+    tm.assert_numpy_array_equal(result, expected)
+
+
+@pytest.mark.parametrize("data", [{}, {"a": []}])
+def test_empty_pyarrow(data):
+    # GH 53155
+    pytest.importorskip("pyarrow", "11.0.0")
+    from pyarrow.interchange import from_dataframe as pa_from_dataframe
+
+    expected = pd.DataFrame(data)
+    arrow_df = pa_from_dataframe(expected)
+    result = from_dataframe(arrow_df)
+    tm.assert_frame_equal(result, expected)
+
+
+def test_multi_chunk_pyarrow() -> None:
+    pa = pytest.importorskip("pyarrow", "11.0.0")
+    n_legs = pa.chunked_array([[2, 2, 4], [4, 5, 100]])
+    names = ["n_legs"]
+    table = pa.table([n_legs], names=names)
+    with pytest.raises(
+        RuntimeError,
+        match="To join chunks a copy is required which is "
+        "forbidden by allow_copy=False",
+    ):
+        pd.api.interchange.from_dataframe(table, allow_copy=False)
+
+
+def test_multi_chunk_column() -> None:
+    pytest.importorskip("pyarrow", "11.0.0")
+    ser = pd.Series([1, 2, None], dtype="Int64[pyarrow]")
+    df = pd.concat([ser, ser], ignore_index=True).to_frame("a")
+    df_orig = df.copy()
+    with pytest.raises(
+        RuntimeError, match="Found multi-chunk pyarrow array, but `allow_copy` is False"
+    ):
+        pd.api.interchange.from_dataframe(df.__dataframe__(allow_copy=False))
+    result = pd.api.interchange.from_dataframe(df.__dataframe__(allow_copy=True))
+    # Interchange protocol defaults to creating numpy-backed columns, so currently this
+    # is 'float64'.
+    expected = pd.DataFrame({"a": [1.0, 2.0, None, 1.0, 2.0, None]}, dtype="float64")
+    tm.assert_frame_equal(result, expected)
+
+    # Check that the rechunking we did didn't modify the original DataFrame.
+    tm.assert_frame_equal(df, df_orig)
+    assert len(df["a"].array._pa_array.chunks) == 2
+    assert len(df_orig["a"].array._pa_array.chunks) == 2
+
+
+def test_timestamp_ns_pyarrow():
+    # GH 56712
+    pytest.importorskip("pyarrow", "11.0.0")
+    timestamp_args = {
+        "year": 2000,
+        "month": 1,
+        "day": 1,
+        "hour": 1,
+        "minute": 1,
+        "second": 1,
+    }
+    df = pd.Series(
+        [datetime(**timestamp_args)],
+        dtype="timestamp[ns][pyarrow]",
+        name="col0",
+    ).to_frame()
+
+    dfi = df.__dataframe__()
+    result = pd.api.interchange.from_dataframe(dfi)["col0"].item()
+
+    expected = pd.Timestamp(**timestamp_args)
+    assert result == expected
+
+
+@pytest.mark.parametrize("tz", ["UTC", "US/Pacific"])
+@pytest.mark.parametrize("unit", ["s", "ms", "us", "ns"])
+def test_datetimetzdtype(tz, unit):
+    # GH 54239
+    tz_data = (
+        pd.date_range("2018-01-01", periods=5, freq="D").tz_localize(tz).as_unit(unit)
+    )
+    df = pd.DataFrame({"ts_tz": tz_data})
+    tm.assert_frame_equal(df, from_dataframe(df.__dataframe__()))
+
+
+def test_interchange_from_non_pandas_tz_aware(request):
+    # GH 54239, 54287
+    pa = pytest.importorskip("pyarrow", "11.0.0")
+    import pyarrow.compute as pc
+
+    if is_platform_windows() and is_ci_environment():
+        mark = pytest.mark.xfail(
+            raises=pa.ArrowInvalid,
+            reason=(
+                "TODO: Set ARROW_TIMEZONE_DATABASE environment variable "
+                "on CI to path to the tzdata for pyarrow."
+            ),
+        )
+        request.applymarker(mark)
+
+    arr = pa.array([datetime(2020, 1, 1), None, datetime(2020, 1, 2)])
+    arr = pc.assume_timezone(arr, "Asia/Kathmandu")
+    table = pa.table({"arr": arr})
+    exchange_df = table.__dataframe__()
+    result = from_dataframe(exchange_df)
+
+    expected = pd.DataFrame(
+        ["2020-01-01 00:00:00+05:45", "NaT", "2020-01-02 00:00:00+05:45"],
+        columns=["arr"],
+        dtype="datetime64[us, Asia/Kathmandu]",
+    )
+    tm.assert_frame_equal(expected, result)
+
+
+def test_interchange_from_corrected_buffer_dtypes(monkeypatch) -> None:
+    # https://github.com/pandas-dev/pandas/issues/54781
+    df = pd.DataFrame({"a": ["foo", "bar"]}).__dataframe__()
+    interchange = df.__dataframe__()
+    column = interchange.get_column_by_name("a")
+    buffers = column.get_buffers()
+    buffers_data = buffers["data"]
+    buffer_dtype = buffers_data[1]
+    buffer_dtype = (
+        DtypeKind.UINT,
+        8,
+        ArrowCTypes.UINT8,
+        buffer_dtype[3],
+    )
+    buffers["data"] = (buffers_data[0], buffer_dtype)
+    column.get_buffers = lambda: buffers
+    interchange.get_column_by_name = lambda _: column
+    monkeypatch.setattr(df, "__dataframe__", lambda allow_copy: interchange)
+    pd.api.interchange.from_dataframe(df)
+
+
+def test_empty_string_column():
+    # https://github.com/pandas-dev/pandas/issues/56703
+    df = pd.DataFrame({"a": []}, dtype=str)
+    df2 = df.__dataframe__()
+    result = pd.api.interchange.from_dataframe(df2)
+    tm.assert_frame_equal(df, result)
+
+
+def test_large_string():
+    # GH#56702
+    pytest.importorskip("pyarrow")
+    df = pd.DataFrame({"a": ["x"]}, dtype="large_string[pyarrow]")
+    result = pd.api.interchange.from_dataframe(df.__dataframe__())
+    expected = pd.DataFrame({"a": ["x"]}, dtype="object")
+    tm.assert_frame_equal(result, expected)
+
+
+def test_non_str_names():
+    # https://github.com/pandas-dev/pandas/issues/56701
+    df = pd.Series([1, 2, 3], name=0).to_frame()
+    names = df.__dataframe__().column_names()
+    assert names == ["0"]
+
+
+def test_non_str_names_w_duplicates():
+    # https://github.com/pandas-dev/pandas/issues/56701
+    df = pd.DataFrame({"0": [1, 2, 3], 0: [4, 5, 6]})
+    dfi = df.__dataframe__()
+    with pytest.raises(
+        TypeError,
+        match=(
+            "Expected a Series, got a DataFrame. This likely happened because you "
+            "called __dataframe__ on a DataFrame which, after converting column "
+            r"names to string, resulted in duplicated names: Index\(\['0', '0'\], "
+            r"dtype='object'\). Please rename these columns before using the "
+            "interchange protocol."
+        ),
+    ):
+        pd.api.interchange.from_dataframe(dfi, allow_copy=False)
+
+
+@pytest.mark.parametrize(
+    ("data", "dtype", "expected_dtype"),
+    [
+        ([1, 2, None], "Int64", "int64"),
+        ([1, 2, None], "Int64[pyarrow]", "int64"),
+        ([1, 2, None], "Int8", "int8"),
+        ([1, 2, None], "Int8[pyarrow]", "int8"),
+        (
+            [1, 2, None],
+            "UInt64",
+            "uint64",
+        ),
+        (
+            [1, 2, None],
+            "UInt64[pyarrow]",
+            "uint64",
+        ),
+        ([1.0, 2.25, None], "Float32", "float32"),
+        ([1.0, 2.25, None], "Float32[pyarrow]", "float32"),
+        ([True, False, None], "boolean", "bool"),
+        ([True, False, None], "boolean[pyarrow]", "bool"),
+        (["much ado", "about", None], "string[pyarrow_numpy]", "large_string"),
+        (["much ado", "about", None], "string[pyarrow]", "large_string"),
+        (
+            [datetime(2020, 1, 1), datetime(2020, 1, 2), None],
+            "timestamp[ns][pyarrow]",
+            "timestamp[ns]",
+        ),
+        (
+            [datetime(2020, 1, 1), datetime(2020, 1, 2), None],
+            "timestamp[us][pyarrow]",
+            "timestamp[us]",
+        ),
+        (
+            [
+                datetime(2020, 1, 1, tzinfo=timezone.utc),
+                datetime(2020, 1, 2, tzinfo=timezone.utc),
+                None,
+            ],
+            "timestamp[us, Asia/Kathmandu][pyarrow]",
+            "timestamp[us, tz=Asia/Kathmandu]",
+        ),
+    ],
+)
+def test_pandas_nullable_with_missing_values(
+    data: list, dtype: str, expected_dtype: str
+) -> None:
+    # https://github.com/pandas-dev/pandas/issues/57643
+    # https://github.com/pandas-dev/pandas/issues/57664
+    pa = pytest.importorskip("pyarrow", "11.0.0")
+    import pyarrow.interchange as pai
+
+    if expected_dtype == "timestamp[us, tz=Asia/Kathmandu]":
+        expected_dtype = pa.timestamp("us", "Asia/Kathmandu")
+
+    df = pd.DataFrame({"a": data}, dtype=dtype)
+    result = pai.from_dataframe(df.__dataframe__())["a"]
+    assert result.type == expected_dtype
+    assert result[0].as_py() == data[0]
+    assert result[1].as_py() == data[1]
+    assert result[2].as_py() is None
+
+
+@pytest.mark.parametrize(
+    ("data", "dtype", "expected_dtype"),
+    [
+        ([1, 2, 3], "Int64", "int64"),
+        ([1, 2, 3], "Int64[pyarrow]", "int64"),
+        ([1, 2, 3], "Int8", "int8"),
+        ([1, 2, 3], "Int8[pyarrow]", "int8"),
+        (
+            [1, 2, 3],
+            "UInt64",
+            "uint64",
+        ),
+        (
+            [1, 2, 3],
+            "UInt64[pyarrow]",
+            "uint64",
+        ),
+        ([1.0, 2.25, 5.0], "Float32", "float32"),
+        ([1.0, 2.25, 5.0], "Float32[pyarrow]", "float32"),
+        ([True, False, False], "boolean", "bool"),
+        ([True, False, False], "boolean[pyarrow]", "bool"),
+        (["much ado", "about", "nothing"], "string[pyarrow_numpy]", "large_string"),
+        (["much ado", "about", "nothing"], "string[pyarrow]", "large_string"),
+        (
+            [datetime(2020, 1, 1), datetime(2020, 1, 2), datetime(2020, 1, 3)],
+            "timestamp[ns][pyarrow]",
+            "timestamp[ns]",
+        ),
+        (
+            [datetime(2020, 1, 1), datetime(2020, 1, 2), datetime(2020, 1, 3)],
+            "timestamp[us][pyarrow]",
+            "timestamp[us]",
+        ),
+        (
+            [
+                datetime(2020, 1, 1, tzinfo=timezone.utc),
+                datetime(2020, 1, 2, tzinfo=timezone.utc),
+                datetime(2020, 1, 3, tzinfo=timezone.utc),
+            ],
+            "timestamp[us, Asia/Kathmandu][pyarrow]",
+            "timestamp[us, tz=Asia/Kathmandu]",
+        ),
+    ],
+)
+def test_pandas_nullable_without_missing_values(
+    data: list, dtype: str, expected_dtype: str
+) -> None:
+    # https://github.com/pandas-dev/pandas/issues/57643
+    pa = pytest.importorskip("pyarrow", "11.0.0")
+    import pyarrow.interchange as pai
+
+    if expected_dtype == "timestamp[us, tz=Asia/Kathmandu]":
+        expected_dtype = pa.timestamp("us", "Asia/Kathmandu")
+
+    df = pd.DataFrame({"a": data}, dtype=dtype)
+    result = pai.from_dataframe(df.__dataframe__())["a"]
+    assert result.type == expected_dtype
+    assert result[0].as_py() == data[0]
+    assert result[1].as_py() == data[1]
+    assert result[2].as_py() == data[2]
+
+
+def test_string_validity_buffer() -> None:
+    # https://github.com/pandas-dev/pandas/issues/57761
+    pytest.importorskip("pyarrow", "11.0.0")
+    df = pd.DataFrame({"a": ["x"]}, dtype="large_string[pyarrow]")
+    result = df.__dataframe__().get_column_by_name("a").get_buffers()["validity"]
+    assert result is None
+
+
+def test_string_validity_buffer_no_missing() -> None:
+    # https://github.com/pandas-dev/pandas/issues/57762
+    pytest.importorskip("pyarrow", "11.0.0")
+    df = pd.DataFrame({"a": ["x", None]}, dtype="large_string[pyarrow]")
+    validity = df.__dataframe__().get_column_by_name("a").get_buffers()["validity"]
+    assert validity is not None
+    result = validity[1]
+    expected = (DtypeKind.BOOL, 1, ArrowCTypes.BOOL, "=")
+    assert result == expected
+
+
+def test_empty_dataframe():
+    # https://github.com/pandas-dev/pandas/issues/56700
+    df = pd.DataFrame({"a": []}, dtype="int8")
+    dfi = df.__dataframe__()
+    result = pd.api.interchange.from_dataframe(dfi, allow_copy=False)
+    expected = pd.DataFrame({"a": []}, dtype="int8")
+    tm.assert_frame_equal(result, expected)

valley/lib/python3.10/site-packages/pandas/tests/interchange/test_spec_conformance.py

@@ -0,0 +1,175 @@
+"""
+A verbatim copy (vendored) of the spec tests.
+Taken from https://github.com/data-apis/dataframe-api
+"""
+import ctypes
+import math
+
+import pytest
+
+import pandas as pd
+
+
+@pytest.fixture
+def df_from_dict():
+    def maker(dct, is_categorical=False):
+        df = pd.DataFrame(dct)
+        return df.astype("category") if is_categorical else df
+
+    return maker
+
+
+@pytest.mark.parametrize(
+    "test_data",
+    [
+        {"a": ["foo", "bar"], "b": ["baz", "qux"]},
+        {"a": [1.5, 2.5, 3.5], "b": [9.2, 10.5, 11.8]},
+        {"A": [1, 2, 3, 4], "B": [1, 2, 3, 4]},
+    ],
+    ids=["str_data", "float_data", "int_data"],
+)
+def test_only_one_dtype(test_data, df_from_dict):
+    columns = list(test_data.keys())
+    df = df_from_dict(test_data)
+    dfX = df.__dataframe__()
+
+    column_size = len(test_data[columns[0]])
+    for column in columns:
+        null_count = dfX.get_column_by_name(column).null_count
+        assert null_count == 0
+        assert isinstance(null_count, int)
+        assert dfX.get_column_by_name(column).size() == column_size
+        assert dfX.get_column_by_name(column).offset == 0
+
+
+def test_mixed_dtypes(df_from_dict):
+    df = df_from_dict(
+        {
+            "a": [1, 2, 3],  # dtype kind INT = 0
+            "b": [3, 4, 5],  # dtype kind INT = 0
+            "c": [1.5, 2.5, 3.5],  # dtype kind FLOAT = 2
+            "d": [9, 10, 11],  # dtype kind INT = 0
+            "e": [True, False, True],  # dtype kind BOOLEAN = 20
+            "f": ["a", "", "c"],  # dtype kind STRING = 21
+        }
+    )
+    dfX = df.__dataframe__()
+    # for meanings of dtype[0] see the spec; we cannot import the spec here as this
+    # file is expected to be vendored *anywhere*;
+    # values for dtype[0] are explained above
+    columns = {"a": 0, "b": 0, "c": 2, "d": 0, "e": 20, "f": 21}
+
+    for column, kind in columns.items():
+        colX = dfX.get_column_by_name(column)
+        assert colX.null_count == 0
+        assert isinstance(colX.null_count, int)
+        assert colX.size() == 3
+        assert colX.offset == 0
+
+        assert colX.dtype[0] == kind
+
+    assert dfX.get_column_by_name("c").dtype[1] == 64
+
+
+def test_na_float(df_from_dict):
+    df = df_from_dict({"a": [1.0, math.nan, 2.0]})
+    dfX = df.__dataframe__()
+    colX = dfX.get_column_by_name("a")
+    assert colX.null_count == 1
+    assert isinstance(colX.null_count, int)
+
+
+def test_noncategorical(df_from_dict):
+    df = df_from_dict({"a": [1, 2, 3]})
+    dfX = df.__dataframe__()
+    colX = dfX.get_column_by_name("a")
+    with pytest.raises(TypeError, match=".*categorical.*"):
+        colX.describe_categorical
+
+
+def test_categorical(df_from_dict):
+    df = df_from_dict(
+        {"weekday": ["Mon", "Tue", "Mon", "Wed", "Mon", "Thu", "Fri", "Sat", "Sun"]},
+        is_categorical=True,
+    )
+
+    colX = df.__dataframe__().get_column_by_name("weekday")
+    categorical = colX.describe_categorical
+    assert isinstance(categorical["is_ordered"], bool)
+    assert isinstance(categorical["is_dictionary"], bool)
+
+
+def test_dataframe(df_from_dict):
+    df = df_from_dict(
+        {"x": [True, True, False], "y": [1, 2, 0], "z": [9.2, 10.5, 11.8]}
+    )
+    dfX = df.__dataframe__()
+
+    assert dfX.num_columns() == 3
+    assert dfX.num_rows() == 3
+    assert dfX.num_chunks() == 1
+    assert list(dfX.column_names()) == ["x", "y", "z"]
+    assert list(dfX.select_columns((0, 2)).column_names()) == list(
+        dfX.select_columns_by_name(("x", "z")).column_names()
+    )
+
+
+@pytest.mark.parametrize(["size", "n_chunks"], [(10, 3), (12, 3), (12, 5)])
+def test_df_get_chunks(size, n_chunks, df_from_dict):
+    df = df_from_dict({"x": list(range(size))})
+    dfX = df.__dataframe__()
+    chunks = list(dfX.get_chunks(n_chunks))
+    assert len(chunks) == n_chunks
+    assert sum(chunk.num_rows() for chunk in chunks) == size
+
+
+@pytest.mark.parametrize(["size", "n_chunks"], [(10, 3), (12, 3), (12, 5)])
+def test_column_get_chunks(size, n_chunks, df_from_dict):
+    df = df_from_dict({"x": list(range(size))})
+    dfX = df.__dataframe__()
+    chunks = list(dfX.get_column(0).get_chunks(n_chunks))
+    assert len(chunks) == n_chunks
+    assert sum(chunk.size() for chunk in chunks) == size
+
+
+def test_get_columns(df_from_dict):
+    df = df_from_dict({"a": [0, 1], "b": [2.5, 3.5]})
+    dfX = df.__dataframe__()
+    for colX in dfX.get_columns():
+        assert colX.size() == 2
+        assert colX.num_chunks() == 1
+    # for meanings of dtype[0] see the spec; we cannot import the spec here as this
+    # file is expected to be vendored *anywhere*
+    assert dfX.get_column(0).dtype[0] == 0  # INT
+    assert dfX.get_column(1).dtype[0] == 2  # FLOAT
+
+
+def test_buffer(df_from_dict):
+    arr = [0, 1, -1]
+    df = df_from_dict({"a": arr})
+    dfX = df.__dataframe__()
+    colX = dfX.get_column(0)
+    bufX = colX.get_buffers()
+
+    dataBuf, dataDtype = bufX["data"]
+
+    assert dataBuf.bufsize > 0
+    assert dataBuf.ptr != 0
+    device, _ = dataBuf.__dlpack_device__()
+
+    # for meanings of dtype[0] see the spec; we cannot import the spec here as this
+    # file is expected to be vendored *anywhere*
+    assert dataDtype[0] == 0  # INT
+
+    if device == 1:  # CPU-only as we're going to directly read memory here
+        bitwidth = dataDtype[1]
+        ctype = {
+            8: ctypes.c_int8,
+            16: ctypes.c_int16,
+            32: ctypes.c_int32,
+            64: ctypes.c_int64,
+        }[bitwidth]
+
+        for idx, truth in enumerate(arr):
+            val = ctype.from_address(dataBuf.ptr + idx * (bitwidth // 8)).value
+            assert val == truth, f"Buffer at index {idx} mismatch"

valley/lib/python3.10/site-packages/pandas/tests/interchange/test_utils.py

@@ -0,0 +1,89 @@
+import numpy as np
+import pytest
+
+import pandas as pd
+from pandas.core.interchange.utils import dtype_to_arrow_c_fmt
+
+# TODO: use ArrowSchema to get reference C-string.
+# At the time, there is no way to access ArrowSchema holding a type format string
+# from python. The only way to access it is to export the structure to a C-pointer,
+# see DataType._export_to_c() method defined in
+# https://github.com/apache/arrow/blob/master/python/pyarrow/types.pxi
+
+
+@pytest.mark.parametrize(
+    "pandas_dtype, c_string",
+    [
+        (np.dtype("bool"), "b"),
+        (np.dtype("int8"), "c"),
+        (np.dtype("uint8"), "C"),
+        (np.dtype("int16"), "s"),
+        (np.dtype("uint16"), "S"),
+        (np.dtype("int32"), "i"),
+        (np.dtype("uint32"), "I"),
+        (np.dtype("int64"), "l"),
+        (np.dtype("uint64"), "L"),
+        (np.dtype("float16"), "e"),
+        (np.dtype("float32"), "f"),
+        (np.dtype("float64"), "g"),
+        (pd.Series(["a"]).dtype, "u"),
+        (
+            pd.Series([0]).astype("datetime64[ns]").dtype,
+            "tsn:",
+        ),
+        (pd.CategoricalDtype(["a"]), "l"),
+        (np.dtype("O"), "u"),
+    ],
+)
+def test_dtype_to_arrow_c_fmt(pandas_dtype, c_string):  # PR01
+    """Test ``dtype_to_arrow_c_fmt`` utility function."""
+    assert dtype_to_arrow_c_fmt(pandas_dtype) == c_string
+
+
+@pytest.mark.parametrize(
+    "pa_dtype, args_kwargs, c_string",
+    [
+        ["null", {}, "n"],
+        ["bool_", {}, "b"],
+        ["uint8", {}, "C"],
+        ["uint16", {}, "S"],
+        ["uint32", {}, "I"],
+        ["uint64", {}, "L"],
+        ["int8", {}, "c"],
+        ["int16", {}, "S"],
+        ["int32", {}, "i"],
+        ["int64", {}, "l"],
+        ["float16", {}, "e"],
+        ["float32", {}, "f"],
+        ["float64", {}, "g"],
+        ["string", {}, "u"],
+        ["binary", {}, "z"],
+        ["time32", ("s",), "tts"],
+        ["time32", ("ms",), "ttm"],
+        ["time64", ("us",), "ttu"],
+        ["time64", ("ns",), "ttn"],
+        ["date32", {}, "tdD"],
+        ["date64", {}, "tdm"],
+        ["timestamp", {"unit": "s"}, "tss:"],
+        ["timestamp", {"unit": "ms"}, "tsm:"],
+        ["timestamp", {"unit": "us"}, "tsu:"],
+        ["timestamp", {"unit": "ns"}, "tsn:"],
+        ["timestamp", {"unit": "ns", "tz": "UTC"}, "tsn:UTC"],
+        ["duration", ("s",), "tDs"],
+        ["duration", ("ms",), "tDm"],
+        ["duration", ("us",), "tDu"],
+        ["duration", ("ns",), "tDn"],
+        ["decimal128", {"precision": 4, "scale": 2}, "d:4,2"],
+    ],
+)
+def test_dtype_to_arrow_c_fmt_arrowdtype(pa_dtype, args_kwargs, c_string):
+    # GH 52323
+    pa = pytest.importorskip("pyarrow")
+    if not args_kwargs:
+        pa_type = getattr(pa, pa_dtype)()
+    elif isinstance(args_kwargs, tuple):
+        pa_type = getattr(pa, pa_dtype)(*args_kwargs)
+    else:
+        pa_type = getattr(pa, pa_dtype)(**args_kwargs)
+    arrow_type = pd.ArrowDtype(pa_type)
+    assert dtype_to_arrow_c_fmt(arrow_type) == c_string