> > What does "unsupported" mean? "Abstract" would look more exact.
> 
> It means they raise io.UnsupportedOperation when called (unless the
> subclass overrides them to do something else).  
> 
> They are not marked with @abstractmethod, so "Abstract" would be
> wrong.

Except that "unsupported" is even more wrong, because it makes it look
like that these methods are not supported by the respective ABCs.
Actually, what happens is that the default implementations are stubs. If
those methods weren't "supported" at all they wouldn't be defined in the
first place.