There's no need to register as Sized -- the Sized ABC recognizes classes that define __len__ automatically. The Container class does the same looking for __contains__. Since the deque class doesn't implement __contains__, it is not considered a Container -- correctly IMO. True. deque doesn't implement __contains__. However "in" still works because of the __iter__ fallback. So from the API's perspective it's still compatible, even though it doesn't implement it. The same probably affects old style iterators (__getitem__ with index). One could argue that
Hi, Guido van Rossum <guido <at> python.org> writes: they are still iterable or containers, but that's harder to check so probably not worth the effort.
Another issue is that builtin types don't accept ABCs currently. For example set() | SomeSet() gives a TypeError, SomeSet() | set() however works.
Pandora's Box -- sure you want to open it?
In 3.0 I'd like to; this was my original intent. In 2.6 I think it's not worth the complexity, though I won't complain. I would love to help on that as I'm very interested in that feature.
Regards, Armin