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