48 lines
966 B
Python
48 lines
966 B
Python
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"""
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Python polyfills for functools
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"""
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import functools
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from collections.abc import Iterable
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from typing import Callable, TypeVar
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from ..decorators import substitute_in_graph
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__all__ = ["reduce"]
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_T = TypeVar("_T")
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_U = TypeVar("_U")
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class _INITIAL_MISSING:
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pass
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# Reference: https://docs.python.org/3/library/functools.html#functools.reduce
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@substitute_in_graph(functools.reduce)
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def reduce(
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function: Callable[[_U, _T], _U],
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iterable: Iterable[_T],
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initial: _U = _INITIAL_MISSING, # type: ignore[assignment]
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/,
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) -> _U:
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it = iter(iterable)
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value: _U
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if initial is _INITIAL_MISSING:
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try:
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value = next(it) # type: ignore[assignment]
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except StopIteration:
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raise TypeError(
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"reduce() of empty iterable with no initial value",
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) from None
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else:
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value = initial
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for element in it:
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value = function(value, element)
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return value
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