[Python-Dev] Check dict implementation details

[Franklin? Lee]

On Sat, Oct 8, 2016 at 6:01 AM, Serhiy Storchaka <storchaka at gmail.com> wrote:
> Since dict is ordered in CPython 3.6, it can be used instead of OrderedDict
> in some places (e.g. for implementing simple limited caches). But since this
> is implementation detail, it can't be used in the stdlib unconditionally.
> Needed a way to check whether dict is ordered.
>
> Actually there are two levels of "ordering".
>
> 1. Dict without deletions is iterated in the order of adding items.
> Raymond's original compact dict implementation satisfied this claim.
>
> 2. In addition the order is preserved after deletion operations. Naoki's
> implementation satisfies this more strong claim.

Sidenote: OrderedDict, unlike dict, is a sequential container (though
not a Sequence), so order matters when doing comparisons, and
OrderedDicts can be reverse-iterated. That might keep dict from
replacing OrderedDict in some cases. Something to keep in mind if this
topic is revisited.