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[Python-Dev] Python 3.6 dict becomes compact and gets a private version; and keywords become ordered

Brett Cannon brett at python.org
Fri Sep 9 12:52:21 EDT 2016 
On Fri, 9 Sep 2016 at 01:58 Antoine Pitrou <solipsis at pitrou.net> wrote:

> On Thu, 8 Sep 2016 14:20:53 -0700
> Victor Stinner <victor.stinner at gmail.com> wrote:
> > 2016-09-08 13:36 GMT-07:00 Guido van Rossum <guido at python.org>:
> > > IIUC there's one small thing we might still want to change somewhere
> > > after 3.6b1 but before 3.6rc1: the order is not preserved when you
> > > delete some keys and then add some other keys. Apparently PyPy has
> > > come up with a clever solution for this, and we should probably adopt
> > > it, but it's probably best not to hurry that for 3.6b1.
> >
> > Very good news: I was wrong, Raymond Hettinger confirmed that the
> > Python 3.6 dict *already* preserves the items order in all cases. In
> > short, Python 3.6 dict = Python 3.5 OrderedDict (in fact, OrderedDict
> > has a few more methods).
>
> Is it an official feature of the language or an implementation detail?
>

It depends on the context. **kwargs is now defined to be an ordered mapping
and PEP 520 has been updated to drop __definition_order__ and to say that
cls.__dict__ is an ordered mapping. Otherwise we have not made dict itself
ordered everywhere.

And there has been discussion to rip out the C code for OrderedDict and
change the Python code to subclass dict so it only has to provide its
additions to the dict API.
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