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"""
Python polyfills for itertools
"""
from __future__ import annotations
import itertools
import sys
from typing import Callable, overload, TYPE_CHECKING, TypeVar
from typing_extensions import TypeAlias
from ..decorators import substitute_in_graph
if TYPE_CHECKING:
from collections.abc import Iterable, Iterator
__all__ = [
"chain",
"chain_from_iterable",
"compress",
"dropwhile",
"islice",
"tee",
"zip_longest",
]
_T = TypeVar("_T")
_U = TypeVar("_U")
_Predicate: TypeAlias = Callable[[_T], object]
_T1 = TypeVar("_T1")
_T2 = TypeVar("_T2")
# Reference: https://docs.python.org/3/library/itertools.html#itertools.chain
@substitute_in_graph(itertools.chain, is_embedded_type=True) # type: ignore[arg-type]
def chain(*iterables: Iterable[_T]) -> Iterator[_T]:
for iterable in iterables:
yield from iterable
@substitute_in_graph(itertools.chain.from_iterable) # type: ignore[arg-type]
def chain_from_iterable(iterable: Iterable[Iterable[_T]], /) -> Iterator[_T]:
return itertools.chain(*iterable)
chain.from_iterable = chain_from_iterable # type: ignore[attr-defined]
# Reference: https://docs.python.org/3/library/itertools.html#itertools.compress
@substitute_in_graph(itertools.compress, is_embedded_type=True) # type: ignore[arg-type]
def compress(data: Iterable[_T], selectors: Iterable[_U], /) -> Iterator[_T]:
return (datum for datum, selector in zip(data, selectors) if selector)
# Reference: https://docs.python.org/3/library/itertools.html#itertools.dropwhile
@substitute_in_graph(itertools.dropwhile, is_embedded_type=True) # type: ignore[arg-type]
def dropwhile(predicate: _Predicate[_T], iterable: Iterable[_T], /) -> Iterator[_T]:
# dropwhile(lambda x: x < 5, [1, 4, 6, 3, 8]) -> 6 3 8
iterator = iter(iterable)
for x in iterator:
if not predicate(x):
yield x
break
yield from iterator
# Reference: https://docs.python.org/3/library/itertools.html#itertools.islice
@substitute_in_graph(itertools.islice, is_embedded_type=True) # type: ignore[arg-type]
def islice(iterable: Iterable[_T], /, *args: int | None) -> Iterator[_T]:
s = slice(*args)
start = 0 if s.start is None else s.start
stop = s.stop
step = 1 if s.step is None else s.step
if start < 0 or (stop is not None and stop < 0) or step <= 0:
raise ValueError(
"Indices for islice() must be None or an integer: 0 <= x <= sys.maxsize.",
)
if stop is None:
# TODO: use indices = itertools.count() and merge implementation with the else branch
# when we support infinite iterators
next_i = start
for i, element in enumerate(iterable):
if i == next_i:
yield element
next_i += step
else:
indices = range(max(start, stop))
next_i = start
for i, element in zip(indices, iterable):
if i == next_i:
yield element
next_i += step
# Reference: https://docs.python.org/3/library/itertools.html#itertools.pairwise
if sys.version_info >= (3, 10):
@substitute_in_graph(itertools.pairwise, is_embedded_type=True) # type: ignore[arg-type]
def pairwise(iterable: Iterable[_T], /) -> Iterator[tuple[_T, _T]]:
a = None
first = True
for b in iterable:
if first:
first = False
else:
yield a, b # type: ignore[misc]
a = b
__all__ += ["pairwise"]
# Reference: https://docs.python.org/3/library/itertools.html#itertools.tee
@substitute_in_graph(itertools.tee)
def tee(iterable: Iterable[_T], n: int = 2, /) -> tuple[Iterator[_T], ...]:
iterator = iter(iterable)
shared_link = [None, None]
def _tee(link) -> Iterator[_T]: # type: ignore[no-untyped-def]
try:
while True:
if link[1] is None:
link[0] = next(iterator)
link[1] = [None, None]
value, link = link
yield value
except StopIteration:
return
return tuple(_tee(shared_link) for _ in range(n))
@overload
def zip_longest(
iter1: Iterable[_T1],
/,
*,
fillvalue: _U = ...,
) -> Iterator[tuple[_T1]]: ...
@overload
def zip_longest(
iter1: Iterable[_T1],
iter2: Iterable[_T2],
/,
) -> Iterator[tuple[_T1 | None, _T2 | None]]: ...
@overload
def zip_longest(
iter1: Iterable[_T1],
iter2: Iterable[_T2],
/,
*,
fillvalue: _U = ...,
) -> Iterator[tuple[_T1 | _U, _T2 | _U]]: ...
@overload
def zip_longest(
iter1: Iterable[_T],
iter2: Iterable[_T],
iter3: Iterable[_T],
/,
*iterables: Iterable[_T],
) -> Iterator[tuple[_T | None, ...]]: ...
@overload
def zip_longest(
iter1: Iterable[_T],
iter2: Iterable[_T],
iter3: Iterable[_T],
/,
*iterables: Iterable[_T],
fillvalue: _U = ...,
) -> Iterator[tuple[_T | _U, ...]]: ...
# Reference: https://docs.python.org/3/library/itertools.html#itertools.zip_longest
@substitute_in_graph(itertools.zip_longest, is_embedded_type=True) # type: ignore[arg-type,misc]
def zip_longest(
*iterables: Iterable[_T],
fillvalue: _U = None, # type: ignore[assignment]
) -> Iterator[tuple[_T | _U, ...]]:
# zip_longest('ABCD', 'xy', fillvalue='-') -> Ax By C- D-
iterators = list(map(iter, iterables))
num_active = len(iterators)
if not num_active:
return
while True:
values = []
for i, iterator in enumerate(iterators):
try:
value = next(iterator)
except StopIteration:
num_active -= 1
if not num_active:
return
iterators[i] = itertools.repeat(fillvalue) # type: ignore[arg-type]
value = fillvalue # type: ignore[assignment]
values.append(value)
yield tuple(values)
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