Shared via mypy Playground

main.py

from typing import Callable, TypeVar


_K = TypeVar("_K")
_V = TypeVar("_V")

class Foo:
    pass

class Util:
    @staticmethod
    def apply(i: str, g: Callable[[str], _K]) -> _K:
        return g(i)

    @staticmethod
    def constructor(_: dict[_K, _V]) -> Foo:
        return Foo()

def proof_of_concept(
    f:  Callable[[int], str],
) -> None:
    Util.constructor(
        {
            f("foo"): f("not_int")
        }
        | Util.apply(
            "", lambda _: {}
        )
    )