classmethodgeneric.py

class MethodType:
    """A Python-equivalent method type that binds type arguments to the calling class."""

    def __init__(self, func: Callable, obj: object) -> None:
        """Initialize this method with the calling class and function."""
        self.__func__ = func
        self.__self__ = obj
        self._generic_classmethod = False

    def __call__(self, *args: object, **kwargs: object) -> object:
        """Call this method with the given arguments and keyword arguments."""
        return self.__func__(self.__self__, *args, **kwargs)

    def __getitem__(self, *values: type) -> None:
        """Bind the type arguments this method was given to the calling class."""
        print(self.__self__)
        if hasattr(self.__self__, "__args__"):
            print(self.__self__.__args__)
        assert all(isinstance(value, type) for value in values), "Type arguments must be types!"
        # https://github.com/python/cpython/blob/0aa0fc3d3ca144f979c684552a56a18ed8f558e4/Lib/typing.py#L1346
        self.__self__.__args__ = values
        return self


class classmethod_generic:
    """A generic classmethod decorator that will allow the method to know its type parameters."""

    def __init__(self, func: Callable) -> None:
        """Initialize the decorator with the supplied classmethod."""
        self.func = func

    def __get__(self, obj: object, cls: object | None = None) -> Callable:
        """Wrap the generic classmethod with a custom method type that knows its type parameters."""
        if cls is None:
            cls = type(obj)
        method = MethodType(self.func, cls)
        method._generic_classmethod = True
        return method