This is indeed a useful extension. I might add it sooner or later
-- sooner if someone contributes a working patch!
> I might imagine that __init__ returns None or self. If it returns self,
> that means construction was ok. If it is None, construction failed.
Not needed -- you can raise an exception.
--Guido van Rossum, CWI, Amsterdam <Guido.van.Rossum@cwi.nl>