Make `frame.f_locals.copy()` return a snapshot dict of `f_locals`

[gaogaotiantian]

Feature or enhancement

Proposal:

Per PEP 667, frame.f_locals is now a write-through proxy (FrameLocalsProxy) for underlying fast local variables. In the beginning we did not implement the copy() method because we think dict(frame.f_locals) is a more explicit way to achieve the snapshot. However, there are existing code that's using frame.f_locals.copy() to take a snapshot. Moreover, types.MappingProxyType({}).copy() returns the copy of the underlying mapping so it's not unprecedented for a proxy.copy() to return a dict.

Thus, we should implement copy() method for FrameLocalsProxy and make it return a dict of snapshot of the current local variables.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/pep-667-consistent-views-of-namespaces/46631/26

Linked PRs

• gh-118921: Add copy() method for FrameLocalsProxy #118923
• [3.13] gh-118921: Add copy() method for FrameLocalsProxy (GH-118923) #118933