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backend/venv/lib/python3.10/site-packages/typing_inspect.py

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+"""Defines experimental API for runtime inspection of types defined
+in the standard "typing" module.
+
+Example usage::
+    from typing_inspect import is_generic_type
+"""
+
+# NOTE: This module must support Python 2.7 in addition to Python 3.x
+
+import sys
+import types
+import typing
+import typing_extensions
+
+from mypy_extensions import _TypedDictMeta as _TypedDictMeta_Mypy
+
+# See comments in typing_extensions source on why the switch is at 3.9.2
+if (3, 4, 0) <= sys.version_info[:3] < (3, 9, 2):
+    from typing_extensions import _TypedDictMeta as _TypedDictMeta_TE
+elif sys.version_info[:3] >= (3, 9, 2):
+    # Situation with typing_extensions.TypedDict is complicated.
+    # Use the one defined in typing_extentions, and if there is none,
+    # fall back to typing.
+    try:
+        from typing_extensions import _TypedDictMeta as _TypedDictMeta_TE
+    except ImportError:
+        from typing import _TypedDictMeta as _TypedDictMeta_TE
+else:
+    # typing_extensions.TypedDict is a re-export from typing.
+    from typing import TypedDict
+    _TypedDictMeta_TE = type(TypedDict)
+
+NEW_TYPING = sys.version_info[:3] >= (3, 7, 0)  # PEP 560
+if NEW_TYPING:
+    import collections.abc
+
+WITH_FINAL = True
+WITH_LITERAL = True
+WITH_CLASSVAR = True
+WITH_NEWTYPE = True
+LEGACY_TYPING = False
+
+if NEW_TYPING:
+    from typing import (
+        Generic, Callable, Union, TypeVar, ClassVar, Tuple, _GenericAlias,
+        ForwardRef, NewType,
+    )
+    from typing_extensions import Final, Literal
+    if sys.version_info[:3] >= (3, 9, 0):
+        from typing import _SpecialGenericAlias
+        typingGenericAlias = (_GenericAlias, _SpecialGenericAlias, types.GenericAlias)
+    else:
+        typingGenericAlias = (_GenericAlias,)
+else:
+    from typing import (
+        Callable, CallableMeta, Union, Tuple, TupleMeta, TypeVar, GenericMeta,
+        _ForwardRef,
+    )
+    try:
+        from typing import _Union, _ClassVar
+    except ImportError:
+        # support for very old typing module <=3.5.3
+        _Union = type(Union)
+        WITH_CLASSVAR = False
+        LEGACY_TYPING = True
+
+    try:  # python 3.6
+        from typing_extensions import _Final
+    except ImportError:  # python 2.7
+        try:
+            from typing import _Final
+        except ImportError:
+            WITH_FINAL = False
+
+    try:  # python 3.6
+        from typing_extensions import Literal
+    except ImportError:  # python 2.7
+        try:
+            from typing import Literal
+        except ImportError:
+            WITH_LITERAL = False
+
+    try:  # python < 3.5.2
+        from typing_extensions import NewType
+    except ImportError:
+        try:
+            from typing import NewType
+        except ImportError:
+            WITH_NEWTYPE = False
+
+
+def _gorg(cls):
+    """This function exists for compatibility with old typing versions."""
+    assert isinstance(cls, GenericMeta)
+    if hasattr(cls, '_gorg'):
+        return cls._gorg
+    while cls.__origin__ is not None:
+        cls = cls.__origin__
+    return cls
+
+
+def is_generic_type(tp):
+    """Test if the given type is a generic type. This includes Generic itself, but
+    excludes special typing constructs such as Union, Tuple, Callable, ClassVar.
+    Examples::
+
+        is_generic_type(int) == False
+        is_generic_type(Union[int, str]) == False
+        is_generic_type(Union[int, T]) == False
+        is_generic_type(ClassVar[List[int]]) == False
+        is_generic_type(Callable[..., T]) == False
+
+        is_generic_type(Generic) == True
+        is_generic_type(Generic[T]) == True
+        is_generic_type(Iterable[int]) == True
+        is_generic_type(Mapping) == True
+        is_generic_type(MutableMapping[T, List[int]]) == True
+        is_generic_type(Sequence[Union[str, bytes]]) == True
+    """
+    if NEW_TYPING:
+        return (isinstance(tp, type) and issubclass(tp, Generic) or
+                isinstance(tp, typingGenericAlias) and
+                tp.__origin__ not in (Union, tuple, ClassVar, collections.abc.Callable))
+    return (isinstance(tp, GenericMeta) and not
+            isinstance(tp, (CallableMeta, TupleMeta)))
+
+
+def is_callable_type(tp):
+    """Test if the type is a generic callable type, including subclasses
+    excluding non-generic types and callables.
+    Examples::
+
+        is_callable_type(int) == False
+        is_callable_type(type) == False
+        is_callable_type(Callable) == True
+        is_callable_type(Callable[..., int]) == True
+        is_callable_type(Callable[[int, int], Iterable[str]]) == True
+        class MyClass(Callable[[int], int]):
+            ...
+        is_callable_type(MyClass) == True
+
+    For more general tests use callable(), for more precise test
+    (excluding subclasses) use::
+
+        get_origin(tp) is collections.abc.Callable  # Callable prior to Python 3.7
+    """
+    if NEW_TYPING:
+        return (tp is Callable or isinstance(tp, typingGenericAlias) and
+                tp.__origin__ is collections.abc.Callable or
+                isinstance(tp, type) and issubclass(tp, Generic) and
+                issubclass(tp, collections.abc.Callable))
+    return type(tp) is CallableMeta
+
+
+def is_tuple_type(tp):
+    """Test if the type is a generic tuple type, including subclasses excluding
+    non-generic classes.
+    Examples::
+
+        is_tuple_type(int) == False
+        is_tuple_type(tuple) == False
+        is_tuple_type(Tuple) == True
+        is_tuple_type(Tuple[str, int]) == True
+        class MyClass(Tuple[str, int]):
+            ...
+        is_tuple_type(MyClass) == True
+
+    For more general tests use issubclass(..., tuple), for more precise test
+    (excluding subclasses) use::
+
+        get_origin(tp) is tuple  # Tuple prior to Python 3.7
+    """
+    if NEW_TYPING:
+        return (tp is Tuple or isinstance(tp, typingGenericAlias) and
+                tp.__origin__ is tuple or
+                isinstance(tp, type) and issubclass(tp, Generic) and
+                issubclass(tp, tuple))
+    return type(tp) is TupleMeta
+
+
+def is_optional_type(tp):
+    """Test if the type is type(None), or is a direct union with it, such as Optional[T].
+
+    NOTE: this method inspects nested `Union` arguments but not `TypeVar` definition
+    bounds and constraints. So it will return `False` if
+     - `tp` is a `TypeVar` bound, or constrained to, an optional type
+     - `tp` is a `Union` to a `TypeVar` bound or constrained to an optional type,
+     - `tp` refers to a *nested* `Union` containing an optional type or one of the above.
+
+    Users wishing to check for optionality in types relying on type variables might wish
+    to use this method in combination with `get_constraints` and `get_bound`
+    """
+
+    if tp is type(None):  # noqa
+        return True
+    elif is_union_type(tp):
+        return any(is_optional_type(tt) for tt in get_args(tp, evaluate=True))
+    else:
+        return False
+
+
+def is_final_type(tp):
+    """Test if the type is a final type. Examples::
+
+        is_final_type(int) == False
+        is_final_type(Final) == True
+        is_final_type(Final[int]) == True
+    """
+    if NEW_TYPING:
+        return (tp is Final or
+                isinstance(tp, typingGenericAlias) and tp.__origin__ is Final)
+    return WITH_FINAL and type(tp) is _Final
+
+
+try:
+    MaybeUnionType = types.UnionType
+except AttributeError:
+    MaybeUnionType = None
+
+
+def is_union_type(tp):
+    """Test if the type is a union type. Examples::
+
+        is_union_type(int) == False
+        is_union_type(Union) == True
+        is_union_type(Union[int, int]) == False
+        is_union_type(Union[T, int]) == True
+        is_union_type(int | int) == False
+        is_union_type(T | int) == True
+    """
+    if NEW_TYPING:
+        return (tp is Union or
+                (isinstance(tp, typingGenericAlias) and tp.__origin__ is Union) or
+                (MaybeUnionType and isinstance(tp, MaybeUnionType)))
+    return type(tp) is _Union
+
+
+LITERALS = {Literal}
+if hasattr(typing, "Literal"):
+    LITERALS.add(typing.Literal)
+
+
+def is_literal_type(tp):
+    if NEW_TYPING:
+        return (tp in LITERALS or
+                isinstance(tp, typingGenericAlias) and tp.__origin__ in LITERALS)
+    return WITH_LITERAL and type(tp) is type(Literal)
+
+
+def is_typevar(tp):
+    """Test if the type represents a type variable. Examples::
+
+        is_typevar(int) == False
+        is_typevar(T) == True
+        is_typevar(Union[T, int]) == False
+    """
+
+    return type(tp) is TypeVar
+
+
+def is_classvar(tp):
+    """Test if the type represents a class variable. Examples::
+
+        is_classvar(int) == False
+        is_classvar(ClassVar) == True
+        is_classvar(ClassVar[int]) == True
+        is_classvar(ClassVar[List[T]]) == True
+    """
+    if NEW_TYPING:
+        return (tp is ClassVar or
+                isinstance(tp, typingGenericAlias) and tp.__origin__ is ClassVar)
+    elif WITH_CLASSVAR:
+        return type(tp) is _ClassVar
+    else:
+        return False
+
+
+def is_new_type(tp):
+    """Tests if the type represents a distinct type. Examples::
+
+        is_new_type(int) == False
+        is_new_type(NewType) == True
+        is_new_type(NewType('Age', int)) == True
+        is_new_type(NewType('Scores', List[Dict[str, float]])) == True
+    """
+    if not WITH_NEWTYPE:
+        return False
+    elif sys.version_info[:3] >= (3, 10, 0) and sys.version_info.releaselevel != 'beta':
+        return (tp in (NewType, typing_extensions.NewType) or
+                isinstance(tp, (NewType, typing_extensions.NewType)))
+    elif sys.version_info[:3] >= (3, 0, 0):
+        try:
+            res = isinstance(tp, typing_extensions.NewType)
+        except TypeError:
+            pass
+        else:
+            if res:
+                return res
+        return (tp in (NewType, typing_extensions.NewType) or
+                (getattr(tp, '__supertype__', None) is not None and
+                 getattr(tp, '__qualname__', '') == 'NewType.<locals>.new_type' and
+                 tp.__module__ in ('typing', 'typing_extensions')))
+    else:  # python 2
+        # __qualname__ is not available in python 2, so we simplify the test here
+        return (tp is NewType or
+                (getattr(tp, '__supertype__', None) is not None and
+                 tp.__module__ in ('typing', 'typing_extensions')))
+
+
+def is_forward_ref(tp):
+    """Tests if the type is a :class:`typing.ForwardRef`. Examples::
+
+        u = Union["Milk", Way]
+        args = get_args(u)
+        is_forward_ref(args[0]) == True
+        is_forward_ref(args[1]) == False
+    """
+    if not NEW_TYPING:
+        return isinstance(tp, _ForwardRef)
+    return isinstance(tp, ForwardRef)
+
+
+def get_last_origin(tp):
+    """Get the last base of (multiply) subscripted type. Supports generic types,
+    Union, Callable, and Tuple. Returns None for unsupported types.
+    Examples::
+
+        get_last_origin(int) == None
+        get_last_origin(ClassVar[int]) == None
+        get_last_origin(Generic[T]) == Generic
+        get_last_origin(Union[T, int][str]) == Union[T, int]
+        get_last_origin(List[Tuple[T, T]][int]) == List[Tuple[T, T]]
+        get_last_origin(List) == List
+    """
+    if NEW_TYPING:
+        raise ValueError('This function is only supported in Python 3.6,'
+                         ' use get_origin instead')
+    sentinel = object()
+    origin = getattr(tp, '__origin__', sentinel)
+    if origin is sentinel:
+        return None
+    if origin is None:
+        return tp
+    return origin
+
+
+def get_origin(tp):
+    """Get the unsubscripted version of a type. Supports generic types, Union,
+    Callable, and Tuple. Returns None for unsupported types. Examples::
+
+        get_origin(int) == None
+        get_origin(ClassVar[int]) == None
+        get_origin(Generic) == Generic
+        get_origin(Generic[T]) == Generic
+        get_origin(Union[T, int]) == Union
+        get_origin(List[Tuple[T, T]][int]) == list  # List prior to Python 3.7
+    """
+    if NEW_TYPING:
+        if isinstance(tp, typingGenericAlias):
+            return tp.__origin__ if tp.__origin__ is not ClassVar else None
+        if tp is Generic:
+            return Generic
+        return None
+    if isinstance(tp, GenericMeta):
+        return _gorg(tp)
+    if is_union_type(tp):
+        return Union
+    if is_tuple_type(tp):
+        return Tuple
+    if is_literal_type(tp):
+        if NEW_TYPING:
+            return tp.__origin__ or tp
+        return Literal
+
+    return None
+
+
+def get_parameters(tp):
+    """Return type parameters of a parameterizable type as a tuple
+    in lexicographic order. Parameterizable types are generic types,
+    unions, tuple types and callable types. Examples::
+
+        get_parameters(int) == ()
+        get_parameters(Generic) == ()
+        get_parameters(Union) == ()
+        get_parameters(List[int]) == ()
+
+        get_parameters(Generic[T]) == (T,)
+        get_parameters(Tuple[List[T], List[S_co]]) == (T, S_co)
+        get_parameters(Union[S_co, Tuple[T, T]][int, U]) == (U,)
+        get_parameters(Mapping[T, Tuple[S_co, T]]) == (T, S_co)
+    """
+    if LEGACY_TYPING:
+        # python <= 3.5.2
+        if is_union_type(tp):
+            params = []
+            for arg in (tp.__union_params__ if tp.__union_params__ is not None else ()):
+                params += get_parameters(arg)
+            return tuple(params)
+        elif is_tuple_type(tp):
+            params = []
+            for arg in (tp.__tuple_params__ if tp.__tuple_params__ is not None else ()):
+                params += get_parameters(arg)
+            return tuple(params)
+        elif is_generic_type(tp):
+            params = []
+            base_params = tp.__parameters__
+            if base_params is None:
+                return ()
+            for bp_ in base_params:
+                for bp in (get_args(bp_) if is_tuple_type(bp_) else (bp_,)):
+                    if _has_type_var(bp) and not isinstance(bp, TypeVar):
+                        raise TypeError(
+                            "Cannot inherit from a generic class "
+                            "parameterized with "
+                            "non-type-variable %s" % bp)
+                    if params is None:
+                        params = []
+                    if bp not in params:
+                        params.append(bp)
+            if params is not None:
+                return tuple(params)
+            else:
+                return ()
+        else:
+            return ()
+    elif NEW_TYPING:
+        if (
+                (
+                    isinstance(tp, typingGenericAlias) and
+                    hasattr(tp, '__parameters__')
+                ) or
+                isinstance(tp, type) and issubclass(tp, Generic) and
+                tp is not Generic):
+            return tp.__parameters__
+        else:
+            return ()
+    elif (
+        is_generic_type(tp) or is_union_type(tp) or
+        is_callable_type(tp) or is_tuple_type(tp)
+    ):
+        return tp.__parameters__ if tp.__parameters__ is not None else ()
+    else:
+        return ()
+
+
+def get_last_args(tp):
+    """Get last arguments of (multiply) subscripted type.
+       Parameters for Callable are flattened. Examples::
+
+        get_last_args(int) == ()
+        get_last_args(Union) == ()
+        get_last_args(ClassVar[int]) == (int,)
+        get_last_args(Union[T, int]) == (T, int)
+        get_last_args(Iterable[Tuple[T, S]][int, T]) == (int, T)
+        get_last_args(Callable[[T], int]) == (T, int)
+        get_last_args(Callable[[], int]) == (int,)
+    """
+    if NEW_TYPING:
+        raise ValueError('This function is only supported in Python 3.6,'
+                         ' use get_args instead')
+    elif is_classvar(tp):
+        return (tp.__type__,) if tp.__type__ is not None else ()
+    elif is_generic_type(tp):
+        try:
+            if tp.__args__ is not None and len(tp.__args__) > 0:
+                return tp.__args__
+        except AttributeError:
+            # python 3.5.1
+            pass
+        return tp.__parameters__ if tp.__parameters__ is not None else ()
+    elif is_union_type(tp):
+        try:
+            return tp.__args__ if tp.__args__ is not None else ()
+        except AttributeError:
+            # python 3.5.2
+            return tp.__union_params__ if tp.__union_params__ is not None else ()
+    elif is_callable_type(tp):
+        return tp.__args__ if tp.__args__ is not None else ()
+    elif is_tuple_type(tp):
+        try:
+            return tp.__args__ if tp.__args__ is not None else ()
+        except AttributeError:
+            # python 3.5.2
+            return tp.__tuple_params__ if tp.__tuple_params__ is not None else ()
+    else:
+        return ()
+
+
+def _eval_args(args):
+    """Internal helper for get_args."""
+    res = []
+    for arg in args:
+        if not isinstance(arg, tuple):
+            res.append(arg)
+        elif is_callable_type(arg[0]):
+            callable_args = _eval_args(arg[1:])
+            if len(arg) == 2:
+                res.append(Callable[[], callable_args[0]])
+            elif arg[1] is Ellipsis:
+                res.append(Callable[..., callable_args[1]])
+            else:
+                res.append(Callable[list(callable_args[:-1]), callable_args[-1]])
+        else:
+            res.append(type(arg[0]).__getitem__(arg[0], _eval_args(arg[1:])))
+    return tuple(res)
+
+
+def get_args(tp, evaluate=None):
+    """Get type arguments with all substitutions performed. For unions,
+    basic simplifications used by Union constructor are performed.
+    On versions prior to 3.7 if `evaluate` is False (default),
+    report result as nested tuple, this matches
+    the internal representation of types. If `evaluate` is True
+    (or if Python version is 3.7 or greater), then all
+    type parameters are applied (this could be time and memory expensive).
+    Examples::
+
+        get_args(int) == ()
+        get_args(Union[int, Union[T, int], str][int]) == (int, str)
+        get_args(Union[int, Tuple[T, int]][str]) == (int, (Tuple, str, int))
+
+        get_args(Union[int, Tuple[T, int]][str], evaluate=True) == \
+                 (int, Tuple[str, int])
+        get_args(Dict[int, Tuple[T, T]][Optional[int]], evaluate=True) == \
+                 (int, Tuple[Optional[int], Optional[int]])
+        get_args(Callable[[], T][int], evaluate=True) == ([], int,)
+    """
+    if NEW_TYPING:
+        if evaluate is not None and not evaluate:
+            raise ValueError('evaluate can only be True in Python >= 3.7')
+        # Note special aliases on Python 3.9 don't have __args__.
+        if isinstance(tp, typingGenericAlias) and hasattr(tp, '__args__'):
+            res = tp.__args__
+            if get_origin(tp) is collections.abc.Callable and res[0] is not Ellipsis:
+                res = (list(res[:-1]), res[-1])
+            return res
+        if MaybeUnionType and isinstance(tp, MaybeUnionType):
+            return tp.__args__
+        return ()
+    if is_classvar(tp) or is_final_type(tp):
+        return (tp.__type__,) if tp.__type__ is not None else ()
+    if is_literal_type(tp):
+        return tp.__values__ or ()
+    if (
+        is_generic_type(tp) or is_union_type(tp) or
+        is_callable_type(tp) or is_tuple_type(tp)
+    ):
+        try:
+            tree = tp._subs_tree()
+        except AttributeError:
+            # Old python typing module <= 3.5.3
+            if is_union_type(tp):
+                # backport of union's subs_tree
+                tree = _union_subs_tree(tp)
+            elif is_generic_type(tp):
+                # backport of GenericMeta's subs_tree
+                tree = _generic_subs_tree(tp)
+            elif is_tuple_type(tp):
+                # ad-hoc (inspired by union)
+                tree = _tuple_subs_tree(tp)
+            else:
+                # tree = _subs_tree(tp)
+                return ()
+
+        if isinstance(tree, tuple) and len(tree) > 1:
+            if not evaluate:
+                return tree[1:]
+            res = _eval_args(tree[1:])
+            if get_origin(tp) is Callable and res[0] is not Ellipsis:
+                res = (list(res[:-1]), res[-1])
+            return res
+
+    return ()
+
+
+def get_bound(tp):
+    """Return the type bound to a `TypeVar` if any.
+
+    It the type is not a `TypeVar`, a `TypeError` is raised.
+    Examples::
+
+        get_bound(TypeVar('T')) == None
+        get_bound(TypeVar('T', bound=int)) == int
+    """
+
+    if is_typevar(tp):
+        return getattr(tp, '__bound__', None)
+    else:
+        raise TypeError("type is not a `TypeVar`: " + str(tp))
+
+
+def get_constraints(tp):
+    """Returns the constraints of a `TypeVar` if any.
+
+    It the type is not a `TypeVar`, a `TypeError` is raised
+    Examples::
+
+        get_constraints(TypeVar('T')) == ()
+        get_constraints(TypeVar('T', int, str)) == (int, str)
+    """
+
+    if is_typevar(tp):
+        return getattr(tp, '__constraints__', ())
+    else:
+        raise TypeError("type is not a `TypeVar`: " + str(tp))
+
+
+def get_generic_type(obj):
+    """Get the generic type of an object if possible, or runtime class otherwise.
+    Examples::
+
+        class Node(Generic[T]):
+            ...
+        type(Node[int]()) == Node
+        get_generic_type(Node[int]()) == Node[int]
+        get_generic_type(Node[T]()) == Node[T]
+        get_generic_type(1) == int
+    """
+
+    gen_type = getattr(obj, '__orig_class__', None)
+    return gen_type if gen_type is not None else type(obj)
+
+
+def get_generic_bases(tp):
+    """Get generic base types of a type or empty tuple if not possible.
+    Example::
+
+        class MyClass(List[int], Mapping[str, List[int]]):
+            ...
+        MyClass.__bases__ == (List, Mapping)
+        get_generic_bases(MyClass) == (List[int], Mapping[str, List[int]])
+    """
+    if LEGACY_TYPING:
+        return tuple(t for t in tp.__bases__ if isinstance(t, GenericMeta))
+    else:
+        return getattr(tp, '__orig_bases__', ())
+
+
+def typed_dict_keys(td):
+    """If td is a TypedDict class, return a dictionary mapping the typed keys to types.
+    Otherwise, return None. Examples::
+
+        class TD(TypedDict):
+            x: int
+            y: int
+        class Other(dict):
+            x: int
+            y: int
+
+        typed_dict_keys(TD) == {'x': int, 'y': int}
+        typed_dict_keys(dict) == None
+        typed_dict_keys(Other) == None
+    """
+    if isinstance(td, (_TypedDictMeta_Mypy, _TypedDictMeta_TE)):
+        return td.__annotations__.copy()
+    return None
+
+
+def get_forward_arg(fr):
+    """
+    If fr is a ForwardRef, return the string representation of the forward reference.
+    Otherwise return None. Examples::
+
+        tp = List["FRef"]
+        fr = get_args(tp)[0]
+        get_forward_arg(fr) == "FRef"
+        get_forward_arg(tp) == None
+    """
+    return fr.__forward_arg__ if is_forward_ref(fr) else None
+
+
+# A few functions backported and adapted for the LEGACY_TYPING context, and used above
+
+def _replace_arg(arg, tvars, args):
+    """backport of _replace_arg"""
+    if tvars is None:
+        tvars = []
+    # if hasattr(arg, '_subs_tree') and isinstance(arg, (GenericMeta, _TypingBase)):
+    #     return arg._subs_tree(tvars, args)
+    if is_union_type(arg):
+        return _union_subs_tree(arg, tvars, args)
+    if is_tuple_type(arg):
+        return _tuple_subs_tree(arg, tvars, args)
+    if is_generic_type(arg):
+        return _generic_subs_tree(arg, tvars, args)
+    if isinstance(arg, TypeVar):
+        for i, tvar in enumerate(tvars):
+            if arg == tvar:
+                return args[i]
+    return arg
+
+
+def _remove_dups_flatten(parameters):
+    """backport of _remove_dups_flatten"""
+
+    # Flatten out Union[Union[...], ...].
+    params = []
+    for p in parameters:
+        if isinstance(p, _Union):  # and p.__origin__ is Union:
+            params.extend(p.__union_params__)  # p.__args__)
+        elif isinstance(p, tuple) and len(p) > 0 and p[0] is Union:
+            params.extend(p[1:])
+        else:
+            params.append(p)
+    # Weed out strict duplicates, preserving the first of each occurrence.
+    all_params = set(params)
+    if len(all_params) < len(params):
+        new_params = []
+        for t in params:
+            if t in all_params:
+                new_params.append(t)
+                all_params.remove(t)
+        params = new_params
+        assert not all_params, all_params
+    # Weed out subclasses.
+    # E.g. Union[int, Employee, Manager] == Union[int, Employee].
+    # If object is present it will be sole survivor among proper classes.
+    # Never discard type variables.
+    # (In particular, Union[str, AnyStr] != AnyStr.)
+    all_params = set(params)
+    for t1 in params:
+        if not isinstance(t1, type):
+            continue
+        if any(isinstance(t2, type) and issubclass(t1, t2)
+               for t2 in all_params - {t1}
+               if (not (isinstance(t2, GenericMeta) and
+                        get_origin(t2) is not None) and
+                   not isinstance(t2, TypeVar))):
+            all_params.remove(t1)
+    return tuple(t for t in params if t in all_params)
+
+
+def _subs_tree(cls, tvars=None, args=None):
+    """backport of typing._subs_tree, adapted for legacy versions """
+    def _get_origin(cls):
+        try:
+            return cls.__origin__
+        except AttributeError:
+            return None
+
+    current = _get_origin(cls)
+    if current is None:
+        if not is_union_type(cls) and not is_tuple_type(cls):
+            return cls
+
+    # Make of chain of origins (i.e. cls -> cls.__origin__)
+    orig_chain = []
+    while _get_origin(current) is not None:
+        orig_chain.append(current)
+        current = _get_origin(current)
+
+    # Replace type variables in __args__ if asked ...
+    tree_args = []
+
+    def _get_args(cls):
+        if is_union_type(cls):
+            cls_args = cls.__union_params__
+        elif is_tuple_type(cls):
+            cls_args = cls.__tuple_params__
+        else:
+            try:
+                cls_args = cls.__args__
+            except AttributeError:
+                cls_args = ()
+        return cls_args if cls_args is not None else ()
+
+    for arg in _get_args(cls):
+        tree_args.append(_replace_arg(arg, tvars, args))
+    # ... then continue replacing down the origin chain.
+    for ocls in orig_chain:
+        new_tree_args = []
+        for arg in _get_args(ocls):
+            new_tree_args.append(_replace_arg(arg, get_parameters(ocls), tree_args))
+        tree_args = new_tree_args
+    return tree_args
+
+
+def _union_subs_tree(tp, tvars=None, args=None):
+    """ backport of Union._subs_tree """
+    if tp is Union:
+        return Union  # Nothing to substitute
+    tree_args = _subs_tree(tp, tvars, args)
+    # tree_args = tp.__union_params__ if tp.__union_params__ is not None else ()
+    tree_args = _remove_dups_flatten(tree_args)
+    if len(tree_args) == 1:
+        return tree_args[0]  # Union of a single type is that type
+    return (Union,) + tree_args
+
+
+def _generic_subs_tree(tp, tvars=None, args=None):
+    """ backport of GenericMeta._subs_tree """
+    if tp.__origin__ is None:
+        return tp
+    tree_args = _subs_tree(tp, tvars, args)
+    return (_gorg(tp),) + tuple(tree_args)
+
+
+def _tuple_subs_tree(tp, tvars=None, args=None):
+    """ ad-hoc function (inspired by union) for legacy typing """
+    if tp is Tuple:
+        return Tuple  # Nothing to substitute
+    tree_args = _subs_tree(tp, tvars, args)
+    return (Tuple,) + tuple(tree_args)
+
+
+def _has_type_var(t):
+    if t is None:
+        return False
+    elif is_union_type(t):
+        return _union_has_type_var(t)
+    elif is_tuple_type(t):
+        return _tuple_has_type_var(t)
+    elif is_generic_type(t):
+        return _generic_has_type_var(t)
+    elif is_callable_type(t):
+        return _callable_has_type_var(t)
+    else:
+        return False
+
+
+def _union_has_type_var(tp):
+    if tp.__union_params__:
+        for t in tp.__union_params__:
+            if _has_type_var(t):
+                return True
+    return False
+
+
+def _tuple_has_type_var(tp):
+    if tp.__tuple_params__:
+        for t in tp.__tuple_params__:
+            if _has_type_var(t):
+                return True
+    return False
+
+
+def _callable_has_type_var(tp):
+    if tp.__args__:
+        for t in tp.__args__:
+            if _has_type_var(t):
+                return True
+    return _has_type_var(tp.__result__)
+
+
+def _generic_has_type_var(tp):
+    if tp.__parameters__:
+        for t in tp.__parameters__:
+            if _has_type_var(t):
+                return True
+    return False