Type dispatch in python

gistfile1.txt

from typing import Callable, Dict, List


def match_signature(signature, args, kwargs):
    ret = True

    args = list(args)
    kwargs = kwargs.copy()

    for name, type_ in signature.__annotations__.items():
        if len(args) > 0:
            # we match the non-keyword arguments first, in order
            if type(args[0]) == type_:
                args.pop(0)
            else:
                return False

        elif name in kwargs:
            # then we match what is left with kw args
            kwargs.pop(name)

    if len(kwargs) == 0:
        return True
    else:
        return False


class typedispatch:
    """
    This class is a decorator that allows to overload functions
    with different type signatures and dynamically call them
    depending on their input arguments
    """

    # class-wide dict to store functions
    functions: Dict[str, List[Callable]] = {}

    def __init__(self, func):
        self.name = func.__name__
        if self.name not in self.functions:
            self.functions[self.name] = []
        self.functions[self.name].append(func)

    def __call__(self, *args, **kwargs):
        for func in self.functions[self.name]:
            if match_signature(func, args, kwargs):
                return func(*args, **kwargs)
        raise ValueError("Matching type signature not found")


if __name__ == "__main__":

    @typedispatch
    def f(x: int, y: int) -> int:
        return x + y

    @typedispatch
    def f(name: str, age: int) -> str:
        return name + f" ({age} y.o.)"

    @typedispatch
    def sub(x: int, y: int) -> int:
        return x - y

    @typedispatch
    def sub(a: str, b: str) -> str:
        return a + b