[Python-3000] Builtin iterator type

[Greg Ewing]

Andrew Koenig wrote:
> Some people in this discussion have suggested that the Pythonic
> way to answer this question is to try to use it as an iterator and see if it
> raises an exception.

That's not what I would say. I would say that you
should design your code so that you don't *need*
to find out whether it's an iterator or not. Instead,
you just require an iterator, always, and trust that
the calling code will give you one. If it doesn't,
your unit tests will catch that. (You *do* have
unit tests, don't you?-)

> I think we should not use inheritance as the
> mechanism for specifying that a particular class has a particular ability.
> I don't know what the mechanism should be, but it shouldn't be inheritance.

Your ability-signallers seem to be something akin to
the Haskell notion of typeclasses. A typeclass is not
itself a type, but represents a set of characteristics
that a type can have.

There have been various proposals before for ways of
registering interfaces outside of the inheritance
hierarchy. It wouldn't be hard to come up with something
if it were thought desirable. I'm still not convinced
that it solves a problem that really needs solving,
however.

--
Greg