[Python-Dev] Guarantee ordered dict literals in v3.7?

[Guido van Rossum]

I'm in favor of stating that dict keeps order as part of the language spec.

However re-reading
https://mail.python.org/pipermail/python-dev/2017-November/150381.html
there's still a point of debate: should it be allowed if dict reorders
after deletion (presumably as a result of a rehash)? I'm in favor of
prescribing that the order should be preserved even in that case, but I
realize there's additional implementation work to be done. Inada-san, what
do you think of this?

--Guido

On Thu, Dec 14, 2017 at 6:03 PM, INADA Naoki <songofacandy at gmail.com> wrote:

> Hi, folks.
>
> TLDR, was the final decision made already?
>
> If "dict keeps insertion order" is not language spec and we
> continue to recommend people to use OrderedDict to keep
> order, I want to optimize OrderedDict for creation/iteration
> and memory usage.  (See https://bugs.python.org/issue31265#msg301942 )
>
> If dict ordering is language spec, I'll stop the effort and
> use remaining time to another optimizations.
>
> My thought is, +1 to make it language spec.
>
> * PHP (PHP 7.2 interpreter is faster than Python) keeps insertion order.
>   So even we make it language spec, I think we have enough room
>   to optimize.
>
> * It can make stop discussion like "Does X keeps insertion order?
>   It's language spec?", "What about Y? Z?".  Everything on top of dict
>   keeps insertion order.  It's simple to learn and explain.
>
> Regards,
> INADA Naoki  <songofacandy at gmail.com>
>
>
> On Sun, Nov 5, 2017 at 3:35 AM, Guido van Rossum <guido at python.org> wrote:
> > This sounds reasonable -- I think when we introduced this in 3.6 we were
> > worried that other implementations (e.g. Jython) would have a problem
> with
> > this, but AFAIK they've reported back that they can do this just fine. So
> > let's just document this as a language guarantee.
> >
> > On Sat, Nov 4, 2017 at 10:30 AM, Stefan Krah <stefan at bytereef.org>
> wrote:
> >>
> >>
> >> Hello,
> >>
> >> would it be possible to guarantee that dict literals are ordered in
> v3.7?
> >>
> >>
> >> The issue is well-known and the workarounds are tedious, example:
> >>
> >>
> >> https://mail.python.org/pipermail/python-ideas/2015-
> December/037423.html
> >>
> >>
> >> If the feature is guaranteed now, people can rely on it around v3.9.
> >>
> >>
> >>
> >> Stefan Krah
> >>
> >>
> >>
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> >
> >
> >
> >
> > --
> > --Guido van Rossum (python.org/~guido)
> >
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>



-- 
--Guido van Rossum (python.org/~guido)
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