composition.py

from typing import Callable

class A: pass
class B: pass
class C: pass

def composition(aToB: Callable[[A], B],
                bToC: Callable[[B], C]) -> Callable[[A], C]:
    """Returns a callable that takes an A and returns a C"""

    def aToC(a: A) -> C:
        return bToC(aToB(a))

    return aToC