[Python-3000] Implementations: A syntax for extending method dispatching beyond type/class inheritance

[Bill Janssen]

> But, looking 
> at the ABC page right now, to implement Dict, I'll need to inherit 
> Mapping and MutableContainer.

Dave, I completely feel your pain.  I think dict is overly complex
(and Mapping).  Almost nobody needs a whole "dict" -- it's become a
grab bag for handy tricks to perform with mapped sets.  After all,
even Container implements a "mapping", via the "get" method.  I think
we need simpler builds on Container that are what people use (without
going down Java's "twisty little maze of twisty little mazes" class
library path).

I also think that the interface to Sequence could be made considerably
simpler by making the Slice object more explicit.  Right now, there's
a lot of syntactic sugar on the interfaces to "dict" and "list", and
that sugar, while useful, is also confusing.

Bill