gh-141510: Use frozendict in the stdlib

[vstinner]

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

[vstinner]

This PR only changes private names, so it should not impact stdlib users.

[vstinner]

If this change is merged, I will propose a follow-up PR which modify public names.

[AlexWaygood]

One optional suggestion in typing.py

[picnixz]

Ok for ssl and a suggestion for opcode

[picnixz]

The values of LOAD_GLOBAL can also be a frozendict (that is, we can have nested frozendicts).

[corona10]

ditto: #144910 (review)

[corona10]

The SC does not allow mechanically replacing all uses of dict. Please wait for reviews from the code owners of each module.

[JelleZijlstra]

What's the benefit of changing this in e.g. typing.py? It might break some users who modify this dict. That's not a supported use case, but we shouldn't go out of our way to break users unless there's some benefit.

[vstinner]

@JelleZijlstra:

What's the benefit of changing this in e.g. typing.py? It might break some users who modify this dict. That's not a supported use case, but we shouldn't go out of our way to break users unless there's some benefit.

The purpose of this change is to prevent dictionary modifications, especially if the modification is done by mistake.

[vstinner]

@JelleZijlstra: Do you prefer that I revert the typing._PROTO_ALLOWLIST change?

[picnixz]

While the variables in stringprep are public, note that the file is autogenerated:

# This file is generated by mkstringprep.py. DO NOT EDIT.

And the docs clearly state:

As a result, these tables are exposed as functions, not as data structures

So, I really think we should consider any direct use or mutation of those variables as really a bad idea and I don't think we should even consider code that messes with that as being legitimate.

[vstinner]

While the variables in stringprep are public, note that the file is autogenerated

I revert the stringprep change to restrict this change to private variables. Changing private variables type should be less controversial than changing public variables type.

[vstinner]

I reverted the typing.py changes. I plan to merge this PR at the end of the week, unless there is a strong reason to not make these changes.

[vstinner]

If someone really want/need to modify one of the frozendict, it remains possible. Example: platform._ver_stages |= frozendict(final=60)

$ ./python
>>> import platform
>>> platform._ver_stages
frozendict({'dev': 10, 'alpha': 20, 'a': 20, 'beta': 30, ..., 'p': 200})

>>> platform._ver_stages['final']=60
...
TypeError: 'frozendict' object does not support item assignment

>>> platform._ver_stages |= frozendict(final=60)
>>> platform._ver_stages
frozendict({'dev': 10, 'alpha': 20, 'a': 20, 'beta': 30, ..., 'p': 200, 'final': 60})

The purpose of this change is more to catch dictionaries modified by accident.

[vstinner]

I merged my PR, thanks for reviews. If someone comes up with an concrete use case to modify one of these private attributes, we can revert the affected attribute.