[Python-3000] Abilities / Interfaces

[Gustavo Niemeyer]

> IMO the difference between ABCs and interfaces/abilities is that
> inserting a new ABC into an existing class hierarchy without modifying
> its source code is considered a hack, and must be done by a helper
> routine that *actually* mucks with __bases__; while (Zope-style)
> interfaces use an external registry or a separate class attribute
> (__implements__) that is intended to be mucked with.

Right.  That and also being able to assign interfaces to individual
instances, being able to split and merge interfaces in a level that
doesn't need changing the implementation itself, and so on.

-- 
Gustavo Niemeyer
http://niemeyer.net