[Python-Dev] Guarantee ordered dict literals in v3.7? (original) (raw)

Guido van Rossum guido at python.org
Thu Dec 14 21:24:50 EST 2017

Oh, I just found https://mail.python.org/pipermail/python-dev/2017-November/150323.html so I already know what you think: we should go with "dicts preserve insertion order" rather than "dicts preserve insertion order until the first deletion". I guess we should wait for Serhiy to confirm that he's okay with this.

On Thu, Dec 14, 2017 at 6:20 PM, Guido van Rossum <guido at python.org> wrote:

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 >> >> >> _>> ________________________ >> Python-Dev mailing list >> Python-Dev at python.org >> https://mail.python.org/mailman/listinfo/python-dev >> Unsubscribe: >> https://mail.python.org/mailman/options/python-dev/guido%40python.org > > > > > -- > --Guido van Rossum (python.org/~guido) > _> ________________________ > Python-Dev mailing list > Python-Dev at python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/songofaca ndy%40gmail.com > -- --Guido van Rossum (python.org/~guido)

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