Comprehension iteration variable overwrite a variable of the same name in the outer scope inside a function with try..except

[Fatal1ty]

Bug report

Checklist

• I am confident this is a bug in CPython, not a bug in a third-party project
• I have searched the CPython issue tracker,
  and am confident this bug has not been reported before

CPython versions tested on:

3.12

Operating systems tested on:

macOS

Output from running 'python -VV' on the command line:

Python 3.12.0rc1 (main, Aug 29 2023, 19:34:25) [Clang 12.0.5 (clang-1205.0.22.9)]

A clear and concise description of the bug:

In the release notes for 3.12.0rc1 there is the following paragraph about comprehension inlining:

Comprehension iteration variables remain isolated; they don’t overwrite a variable of the same name in the outer scope, nor are they visible after the comprehension. This isolation is now maintained via stack/locals manipulation, not via separate function scope.

I found a case when a comprehension iteration variable overwrite a variable of the same name in the outer scope:

def foo(value):
    try:
        {int(key): value for key, value in value.items()}
    except:
        print(repr(value))  # will print 'baz' instead of {'bar': 'baz'}
foo({'bar':'baz'})

However, if you run this code outside of the function, isolation works:

value = {'bar': 'baz'}
try:
    {int(key): value for key, value in value.items()}
except:
    print(repr(value))  # ok, it will print {'bar': 'baz'}

Linked PRs

• gh-108654: restore comprehension locals before handling exception #108659
• [3.12] gh-108654: restore comprehension locals before handling exception (GH-108659) #108700

[Eclips4]

cc @carljm

[AlexWaygood]

This looks completed, but please reopen if not @carljm!

[Fatal1ty]

I can confirm that it's fixed it 3.12.0rc2 🎉