inheritance for multiprocessing.managers.DictProxy

[tungol]

Similar to #12873 and #12892

DictProxy doesn't inherit from MutableMapping and it isn't registered to it either. It does have all the relevant methods.

[tungol]

I'm honestly kind of surprised all three of these turned out to be "no effect".

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[AlexWaygood]

I'm honestly kind of surprised all three of these turned out to be "no effect".

I think they're used somewhat rarely; I wouldn't be surprised if there's no mypy_primer coverage for them. They are used, though; we've had bug reports in the past about them when I caused a regression.

[tungol]

That makes sense.

[srittau]

I'm in favor of changes like this, especially when there's no primer impact. It's also a chance to steer users towards using protocols. (In the long term we should also look into adding some "mapping light" protocols to typing. Similar to what I suggested for Reader/Writer protocols (which I need to prepare a PR for).)

[AlexWaygood]

I'm a bit nervous about this, because sort-of the whole point of this class is that it's meant to be basically drop-in compatible with dict. I think it almost certainly should be registered to the ABC at runtime :/

[tungol]

I've opened a cpython issue and MR to get this and BaseListProxy registered to their ABCs at runtime.

python/cpython#126417

python/cpython#126419

[tungol]

This is now fixed in cpython for 3.12 and up. It probably doesn't make sense to branch for the sake of 3.8 to 3.11.