[Python-3000] Traits/roles instead of ABCs

[Bill Janssen]

> On 30/04/07, Bill Janssen <janssen at parc.com> wrote:
> > > 6) that doesn't freeze all of the key APIs in concrete
> >
> > After 15 years of experience with the key APIs, we could perhaps freeze some of
> > them?
> 
> After 15 years not being able to clearly state what "file-like" or
> "mapping-like" means to different people, perhaps we should accept
> that there is no clear-cut answer...?

And that's a problem -- people are confused.  Instead of throwing up
our hands, I think we should define what "file-like" means.

> > In other words, what APIs does this value support?
> > In other words, what APIs does this value support?
> > In other words, what APIs does this value support?
> 
> Yes, but the ABC proposal is about establishing a vocabulary for
> answering those questions, not about asking them.

That's what "isinstance" does.  The mechanism for asking is already
there; we're just trying to standardize a few answers.

And, by the way, I'm not sure adding the ability to override
"isinstance" is a good idea.

Bill