python decorator that cast argument type

strict.py

from typing import Any, Callable, TypeVar, Type, cast, Union, Protocol
from functools import singledispatchmethod

T = TypeVar("T", int, str)


def stricttype(
    type_: Type[T],
) -> Callable[[Callable[[Any, Any], None]], Callable[[Any, T], None]]:
    def inner(method: Callable[[Any, Any], None]) -> Callable[[Any, T], None]:
        return method

    return inner


T_contra = TypeVar("T_contra", contravariant=True)


class StrictDispatch(Protocol[T_contra]):
    def __call__(self, arg: T_contra) -> None:
        ...

    def register(self, cls: Any, method: Any = None) -> None:
        ...


def strictsingledispatchmethod(
    type_: T_contra,
) -> Callable[[singledispatchmethod], StrictDispatch[T_contra]]:
    def inner(
        method: singledispatchmethod,
    ) -> StrictDispatch[T_contra]:
        return cast(StrictDispatch[T_contra], method)

    return inner


Event = Union[int, str]


class Foo:
    @stricttype(type_=int)
    def hoge(self, arg: Any) -> None:
        print("hoge")

    @stricttype(type_=str)
    def foo(self, arg: Any) -> None:
        print("foo")

    @strictsingledispatchmethod(type_=Event)
    @singledispatchmethod
    def dispatch(self, arg: Any) -> None:
        print("dispatch")

    @dispatch.register
    def _dispatch_int(self, arg: int) -> None:
        print("dispatch int", arg)

    @dispatch.register
    def _dispatch_str(self, arg: str) -> None:
        print("dispatch str", arg)


foo = Foo()
foo.hoge(100)
foo.dispatch(100)
foo.dispatch("100")
foo.dispatch("fooooobar")
foo.dispatch("100")