[issue40116] Regression in memory use of shared key dictionaries for "compact dicts"

[Marc-Andre Lemburg]

Marc-Andre Lemburg <mal at egenix.com> added the comment:

On 22.09.2021 21:02, Raymond Hettinger wrote:
>> The language specification says that the dicts maintain insertion 
>> order, but the wording implies that this only to explicit 
>> dictionaries, not instance attribute or other namespace dicts.
> 
> That is a quite liberal reading of the spec.  I would object to making instance and namespace dicts behave differently.  That would be a behavior regression and we would forever have to wrestle with the difference.

I agree. Keeping the insertion order is essential for many common
use cases, including those where a class or instance dict is used,
e.g. namespaces used for data records, data caches, field
definitions in data records, etc. (and yes, those often can be
dynamically extended as well :-)).

I think for the case you mention, a documentation patch would be
better and more helpful for the programmers. Point them to slots
and the sharing problem should go away in most cases :-)

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nosy: +lemburg

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