(original) (raw)

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@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@gmail.com>

On Sun, Nov 5, 2017 at 3:35 AM, Guido van Rossum <guido@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@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)