[Python-Dev] type categories

[Guido van Rossum]

> I'm leary of trying to weave some interface taxonomy into the standard
> library and types without having a lot of experience in using this for
> real world applications.  Even then, it's possible <wink> that there
> will be a lot of disagreement on the shape of the type hierarchy.

That's what I said when I predicted it would be hard to come up with
an ontology. :-)

> So one strategy would be to not classify the existing types and
> classes ahead of time, but to provide a way for an application to
> declare conformance to existing types in a way that makes sense for
> the application (or library).  The downside of this is that it may
> lead to a raft of incompatible interface declarations, but I also
> think that eventually we'd see convergence as we gain more experience.

This is what Zope does.  One problem is that it has its own notion of
what makes a "sequence", a "mapping", etc. that don't always match the
Pythonic convention.

> My guess would be that of all the interfaces that get defined and used
> in the Python community, on a few that are commonly agreed on or
> become ubiquitous idioms will migrate into the core.  I don't think we
> need to solve this "problem" for the core types right away.  Let's
> start by providing mechanism and not policy.

Sure.  But does that mean the mechanism needs to be necessarily
separate from the inheritance mechanism?

--Guido van Rossum (home page: http://www.python.org/~guido/)