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[3.12] gh-105256: What's New note for comprehension over locals() (GH-106378) #106471

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Jul 6, 2023
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[3.12] gh-105256: What's New note for comprehension over locals() (GH-106378) #106471

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6 changes: 6 additions & 0 deletions Doc/whatsnew/3.12.rst
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Expand Up @@ -253,6 +253,12 @@ Inlining does result in a few visible behavior changes:
* Calling :func:`locals` inside a comprehension now includes variables
from outside the comprehension, and no longer includes the synthetic ``.0``
variable for the comprehension "argument".
* A comprehension iterating directly over ``locals()`` (e.g. ``[k for k in
locals()]``) may see "RuntimeError: dictionary changed size during iteration"
when run under tracing (e.g. code coverage measurement). This is the same
behavior already seen in e.g. ``for k in locals():``. To avoid the error, first
create a list of keys to iterate over: ``keys = list(locals()); [k for k in
keys]``.

Contributed by Carl Meyer and Vladimir Matveev in :pep:`709`.

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