splitby.py

import typing
from functools import lru_cache

T = typing.TypeVar("T")
PredicateFunction = typing.Callable[[T], bool]
SourceIterable = typing.Iterable[T]
ObjectList = typing.List[T]


def splitby(
        pred: PredicateFunction,
        seq: SourceIterable
) -> typing.Tuple[ObjectList, ObjectList]:
    """Function to apply a predicate function to a sequence of items, and return lists of
    values where the predicate returns True and values where the predicate returns False.
    """
    ret = ([], [])
    pred_with_cache = lru_cache(pred)
    for ob in seq:
        ret[not pred_with_cache(ob)].append(ob)
    return ret


if __name__ == '__main__':
    def is_odd(x):
        return bool(x % 2)

    odds, evens = splitby(is_odd, range(10))
    print(evens)
    print(odds)

    # [0, 2, 4, 6, 8]
    # [1, 3, 5, 7, 9]