[Python-Dev] type categories

Guido van Rossum guido@python.org
Fri, 13 Sep 2002 01:08:22 -0400

> > > A few weeks ago I realized there was reason in principle that
> >                                    ^^^^^^^^^^
> > Did you mean "was no reason"???

So did you?

> > > declaring a class satisfies an interface shouldn't just amount to
> > > adding the interface to the class' __bases__ (as Guido has been
> > > suggesting all along).
> > >
> > > Why not? Am we missing somethings?
> >
> > We'd need a trick to deny an interface that would be inherited by
> > default.  Something like private inheritance.
> I think it's more than that. You might need to "uninherit": Say
> Interface A begets class B which begets class C. What if C doesn't
> fulfill A?

Sorry, I meant to include that case.  How do you do that in C++?
Inherit privately from B and publicly from A, and making A virtual
base everywhere?

> > There's also the ambiguity of inheriting from a single interface: does
> > that create a sub-interface or an implementation of the interface?
> > Of course with your C++ hat on you probably don't care.  On Mondays,
> > Wednesdays, Fridays and alternating Sundays I don't care either.
> With my C++ hat on I can't even imagine this. In C++ we don't
> express interfaces in code: they're written down as "concepts" in
> the some documentation somewhere (no, I don't think an abstract
> class in C++ is a good analogy for these Python interfaces).

What's the difference between an abstract class and an interface in

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