[Python-Dev] PEP 246: lossless and stateless

[Just van Rossum]

Phillip J. Eby wrote:

> >But it _does_ perform an implicit adaptation, via PyObject_GetIter.
> 
> First, that's not implicit.  Second, it's not adaptation, either. 
> PyObject_GetIter invokes the '__iter__' method of its target -- a
> method that is part of the *iterable* interface.  It has to have
> something that's *already* iterable; it can't "adapt" a non-iterable
> into an iterable.
> 
> Further, if calling a method of an interface that you already have in
> order to get another object that you don't is adaptation, then what
> *isn't* adaptation?  Is it adaptation when you call 'next()' on an
> iterator? Are you then "adapting" the iterator to its next yielded
> value?

That's one (contrived) way of looking at it. Another is that

  y = iter(x)

adapts the iterable protocol to the iterator protocol. I don't (yet) see
why a bit of state disqualifies this from being called adaptation.

> No?  Why not?  It's a special method of the "iterator" interface,
> just like __iter__ is a special method of the "iterable" interface.

The difference it that the result of .next() doesn't have a specified
interface.

> So, I can't see how you can call one adaptation, but not the other. 
> My conclusion: neither one is adaptation.

Maybe...

Just