utils.py

from typing import TypeVar, Any, Generic, cast, Optional, Type
import functools

T = TypeVar("T")


class class_method_variant(Generic[T]):
    def __init__(self, class_method_name):
        self.class_method_name = class_method_name

    method: Any

    def __call__(self, method: T) -> T:
        self.method = method
        return cast(T, self)

    def __get__(self, obj, objtype: Optional[Type[Any]] = None):
        @functools.wraps(self.method)
        def _wrapper(*args, **kwargs):
            if obj is not None:
                # Method was called as an instance method, e.g.
                # instance.method(...)
                return self.method(obj, *args, **kwargs)
            elif len(args) > 0 and objtype is not None and isinstance(args[0], objtype):
                # Method was called as a class method with the instance as the
                # first argument, e.g. Class.method(instance, ...) which in
                # Python is the same thing as calling an instance method
                return self.method(args[0], *args[1:], **kwargs)
            else:
                # Method was called as a class method, e.g. Class.method(...)
                class_method = getattr(objtype, self.class_method_name)
                return class_method(*args, **kwargs)

        return _wrapper