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

[François Pinard]

> > I'm happy to add the text, but i want to be clear, then: is it
> > acceptable to write an iterator that only provides <next> if you
> > only care about the "iteration protocol" and not the "for-able
> > protocol"?

> No, an iterator ought to provide both, but it's good to recognize that
> there *are* two protocols.

> >     A class is a valid iterator object when it defines a next()
> >     method that behaves as described above.  A class that wants
> >     to be an iterator also ought to implement __iter__()
> >     returning itself.

> I would like to see this strengthened.  I envision "iterator algebra"
> code that really needs to be able to do a for loop over an iterator
> when it feels like it.

Maybe the reasons behind having __iter__() returning itself should be
clearly expressed in the PEP, too.  On this list, Tim gave one recently,
Guido gives another here, but unless I missed it, the PEP gives none.
Usually, PEPs explain the reasons behind the choices.

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