[Python-Dev] Re: Single- vs. Multi-pass iterability

[François Pinard]

[Greg Ewing]

> pinard@iro.umontreal.ca:

> > could we have the guarantee that if an iterable returns an
> > iterator through the iterable's __iter__, the iterator's __iter__ method
> > will never be called from looping over the iterable?

> [...pause while Greg's brain parses that sentence...]

(Sorry for my bad English.)

> Yes, I believe that's true.

If yes, then, the Library Reference is misleading, at the page:

   http://www.python.org/dev/doc/devel/lib/typeiter.html

when it strongly says that any iterator's __iter__ method is "required".
I guess this is a possible source of confusion.

The context does not make it clear that the iterator's __iter__ method is
*only* required whenever one *also* wants to use an iterator as an iterable.
Better would be to describe __iter__ only once, the first time through,
saying everything there that has to be said, and only retain for iterators
the requirement of having a `next()' method.  We should describe the truth.

P.S. - Also, I do not understand the tiny bit about the `in' statement in the
above page.  Has `in' ever been a statement?  If it refers to the comparison
operator `in', then has it any special properties when used with iterators?
I'm unsuccessful at seeing any hint about this from the documentation:

   http://www.python.org/dev/doc/devel/ref/comparisons.html

-- 
François Pinard   http://www.iro.umontreal.ca/~pinard