On Tue, May 27, 2008 at 12:16 PM, Armin Ronacher <armin.ronacher@active-4.com> wrote:
Hi,
Guido van Rossum <guido <at> python.org> writes:
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.
Sure, but that fallback is slow, and intentionally does not trigger the 'Container' ABC.
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 they are still iterable or containers, but that's harder to check so probably not worth the effort.
The ABCs do not intend to capture partial behavioral compatibility that way -- the intent is to capture interface (in the duck typing sense). Whether __iter__ is a good enough substitute for __contains__ depends on a lot of things -- surely for a huge list it isn't, and for an iterator it isn't either (since it modifies the iterator's state).
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.
Please do submit patches! -- --Guido van Rossum (home page: http://www.python.org/~guido/)