Pasting the relevant snippet from your link: def __subclasshook__(cls, C): if cls is Iterable: if any("__iter__" in B.__dict__ for B in C.__m

Pasting the relevant snippet from your link: def __subclasshook__(cls, C): if cls is Iterable: if any("__iter__" in B.__dict__ for B in C.__mro__): return True return NotImplemented Wow, hadn't seen this before. That's exactly what I mean. If I can define my own, e.g. Addable, which does a similar check for the presence of __add__ (and __radd__) and MyPy uses the subclasshook, then that'd be perfect.