[Python-Dev] PEP 469: Restoring the iterkeys/values/items() methods

[Devin Jeanpierre]

On Sun, Apr 20, 2014 at 12:27 PM, Kristján Valur Jónsson
<kristjan at ccpgames.com> wrote:
> Well, "for i in x" and other iteration constructs already call "iter ()" on
> their iterable. That's the point. Unless you want to manually iterate using
> "next ()" then the distinction between an iterable and an iterator is
> academic.

Or unless you iterate over the same thing multiple times, which can happen.

P.S.: If Python had intended to support 2.x/3.x polyglots in the first
place, would iteritems etc. have been removed? My feeling is "no", in
which case they should be re-added, since this is the main supported
porting mechanism going forward.

-- Devin


> -------- Original message --------
> From: Steven D'Aprano
> Date:20/04/2014 17:05 (GMT+00:00)
> To: python-dev at python.org
> Subject: Re: [Python-Dev] PEP 469: Restoring the iterkeys/values/items()
> methods
>
> On Sun, Apr 20, 2014 at 03:07:39PM +0000, Kristján Valur Jónsson wrote:
>
>> Does one ever use iteritems() et al without first invoking iter() on
>> it?
>
> I can't speak for others, but I never invoke iteritems *with* iter().
> What would be the point? iteritems is documented as returning an
> interator.
>
> # never this
> for key, value in iter(mydict.iteritems()): ...
>
> # but this
> for key, value in mydict.iteritems(): ...
>
>
>> I.e. is it important that it is an iterator, rather than an
>> iterable? I think we could easily relax that requirement in the pep
>> and solve 99% of the use cases.
>
> And the other 1% of cases would be a land-mine waiting to blow the
> user's code up.
>
> Would it actually solve 99% of the use cases? Or only 90%? Or 50%? How
> do you know?
>
> In Python 2.7 iteritems() etc is documented as returning an iterator.
> That's a promise of the language, and people will rely on it. But they
> won't be able to rely on that promise in polygot 2+3 code -- exactly the
> use-case this PEP is trying to satisfy -- because the promise to return
> an iterator will be broken in 3.
>
> It would be actively misleading, since Python 3's iteritems() would
> return a view, not an iter, and it would fail at solving the backwards
> compatibility issue since views and iterators are not interchangeable
> except for the most basic use of iteration.
>
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