Note: at the time this event is called, the new class has not yet been created. The functions in post_funcs will be called after the class is created, with the single arguments of (new_class). Also, early_funcs will be called at the soonest possible time after class creation (post_funcs is called after the class's __classinit__).
Abstract classes can override this to customize issubclass().
This is invoked early on by abc.ABCMeta.__subclasscheck__(). It should return True, False or NotImplemented. If it returns NotImplemented, the normal algorithm is used. Otherwise, it overrides the normal algorithm (and the outcome is cached).
See the source for more information.