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

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

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.

That makes sense.

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 :/

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

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.