object.__reduce__ might return a string

[MSeifert04]

I have a type which returns a string in __reduce__ which leads to a mypy failure:

Return type "str" of "__reduce__" incompatible with return type "Tuple[Any, ...]" in supertype "object"

According to the __reduce__ documentation this method can return a string or a Tuple.

Would it make sense to change the typing to __reduce__(self) -> Union[str, Tuple[Any, ...]]: ...?

[srittau]

Same for __reduce_ex__. Makes sense, PR welcome!