[Python-3000] Builtin iterator type

[Greg Ewing]

George Sakkis wrote:

> class Container(object):
>
> class Sequence(Container):

> class Mapping(Container):
>
> Note that this does _not_ disallow duck typing; anyone is perfectly
> free to define a method len() in a class that does not extend any of
> the above so that a client can call x.len() successfully.

What's the point, then? What benefit do I get from
extending Sequence if I can achieve the same thing
without bothering?

--
Greg