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main.py

import typing as tp


class Wrapped[**P, T]:
    def __call__(self, *args: P.args, **kwargs: P.kwargs) -> T:
        raise NotImplementedError


def inner[**P, T](f: tp.Callable[P, T]) -> Wrapped[P, T]:
    assert False


class K:
    @inner
    def f(self, x: int):
        return x

    def g(self, x: int):
        return x


a = K()
a.g(2)
a.f(2)  # fails with x missing