Decorator to add functions as methods to a class (Note: This is basically useless as you can just use `method_name = function` inside the class body)

function_to_method.py

from typing import TypeVar, Union, Callable, Optional


_ClsT = TypeVar('_ClsT', bound=type)


def add_method(func: Union[Callable, classmethod, staticmethod],
               name: Optional[str] = None) -> Callable[[_ClsT], _ClsT]:
    """Class decorator that adds the given function as a method to the class"""

    def decorator(cls: _ClsT) -> _ClsT:
        nonlocal name
        if name is not None:
            pass
        elif isinstance(func, classmethod) or isinstance(func, staticmethod):
            name = func.__func__.__name__
        else:
            name = func.__name__
        if hasattr(cls, name):
            raise ValueError(f'method name conflict: {name}')
        setattr(cls, name, func)
        return cls

    return decorator