[Python-Dev] ABC issues

[Armin Ronacher]

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.  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.

> >> 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