pythongh-105256: What's New note for comprehension over locals()

carljm · carljm · commit 3afb538676e7 · 2023-07-03T14:37:56.000-07:00
diff --git a/Doc/whatsnew/3.12.rst b/Doc/whatsnew/3.12.rst
@@ -253,6 +253,11 @@ 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 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 shown by 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`.
 
