Functional Programming with type annotation in Python

fp_with_types.py

from typing import Callable, Iterable, TypeVar, Iterator, Optional

A = TypeVar("A")


def some(pred: Callable[[A], bool], seq: Iterable[A]) -> Optional[A]:
    """
    Returns the first item in "seq" that satisfies "pred".

    Examples:
        fp.some(lambda x: x > 2, [1, 0, 3, 2])
        > 3
        fp.some(lambda x: x > 2, [1, 0, 2, 2])
        > None
    """
    def recur(seqiter: Iterator[A]) -> Optional[A]:
        try:
            item = next(seqiter)
        except StopIteration:
            return None
        return item if pred(item) else recur(seqiter)
    return recur(iter(seq))