Document FrameLocalsProxy behaviour quirks

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
88/100
Issue type
Documentation
Clarity
Clearly specified
Activity status
Active
Tech stack
python
Domain
documentation

Research direction

Start with the frame objects section in the Python data model documentation and review PEP 667, including the linked PEP pull request. Add a fourth subsection describing the five listed FrameLocalsProxy behaviours and a see-also link back to PEP 667. Done means the main docs explain proxy identity, shared extra keys, undeletable locals, and dict-producing APIs.

Written by the indexing model from the issue text.

Description

3.13 3.14 docs triaged

Following PEP 667, https://docs.python.org/dev/reference/datamodel.html#frame-objects mentions that frame.f_locals may be a write-through proxy object, but doesn't really explain what that means.

Once https://github.com/python/peps/pull/3845 lands PEP 667 will contain such a description, but the main docs should at least cover the key behaviours:

  • new instance on every attribute access
  • two proxies with the same keys and values will still be unequal if they refer to different frames
  • extra keys can be stored and are stored on the frame itself so they're shared across all proxies for the same frame
  • keys corresponding to local variables can't be deleted
  • .copy() (and any other API that produces a new container) returns a regular dict instance

Suggested location would be as a new 4th subsection under the frame objects section linked above. A "see also" from that new subsection back to PEP 667 would also be a useful addition.

Linked PRs
  • gh-157869
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