[WIP] gh-141510: PEP 814: Add built-in frozendict type

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• Basic tests
• Bare minimum documentation
• Support frozendict in marshal, pickle, json, copy
• Replace dict with frozendict in many stdlib modules

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📚 Documentation preview 📚: https://cpython-previews--141508.org.readthedocs.build/

• Issue: PEP 814: Add built-in frozendict type #141510

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This PR was created mainly to play with PEP 814 implementation, not to be merged.

If PEP 814 is accepted, this PR should be splitted into smaller parts, easier to review.

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mypy / Run mypy on Lib/_pyrepl (pull_request)
mypy / Run mypy on Lib/tomllib (pull_request)

mypy fails with Name "frozendict" is not defined.

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Tests / Android (x86_64) (pull_request) does crash, I'm not sure why.

  0:01:27 [ 39/497] test.test_concurrent_futures.test_interpreter_pool
  E/libsigchain: reverting to SIG_DFL handler for signal 11, ucontext 0x72d5b7547ac0

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Tests / Android (x86_64) (pull_request) does crash, I'm not sure why.

It should be fixed by Add PyFrozenDict_Type to static_types commit.

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TODO: Provide better error on hashing a mutable value:

>>> fd = frozendict(x=[1])
>>> hash(fd)
...
TypeError: cannot use 'tuple' as a set element (unhashable type: 'list')

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This PR is a draft combining all changes to adopt frozendict in the stdlib. It's too big to be merged. I started to split this PR into smaller PRs with #144757 as a starting point: most basic PR just to add the frozendict type.

[benediktjohannes]

@vstinner is it purposed that this draft PR is linked in the documentation at „reference implementation“ in PEP 814? I know that this includes more than the other PR, but I think that it was probably better to link the real PRs with the real changes made because they include really every single change correctly rather than a draft, no?

[hugovk]

@benediktjohannes PEPs are historical documents (PEP 814 will soon have a banner to this effect), so it's fine for https://peps.python.org/pep-0814/#reference-implementation to point to this PR. It was the reference implementation at the time the PEP was written, discussed and accepted.

The real implementation is another matter, and is being committed in smaller PRs. We can follow along via the issue, #141510.

[benediktjohannes]

Thanks!

[vstinner]

I started to split this PR into smaller PRs with #144757 as a starting point: most basic PR just to add the frozendict type.

I created many PRs in #141510. This PR is no longer needed, I close it.