Typed compose

typed_compose.py

from typing import Callable, TypeVar

T = TypeVar('T')
T2 = TypeVar('T2')
T3 = TypeVar('T3')


def compose(func1: Callable[[T], T2],
            func2: Callable[[T3], T]) -> Callable[[T3], T2]:
    def inner(arg: T3) -> T2:
        return func1(func2(arg))
    return inner


def plus2(x: int) -> int:
    return x + 2


def minus2(x: int) -> float:
    return float(x - 2)


add0_plus_first = compose(minus2, plus2)
add0_minus_first = compose(plus2, minus2)