UnboundLocalError when module is shadowed by a comprehension and then accessed by another comprehension

[jmymay]

Bug report

Bug description:

Seems to be a regression in 3.12 when compared to 3.11, likely caused by PEP 709: Comprehension inlining, but I haven't verified this. Example below. (Noticed while running this code.)

import sys
def f():
    _ = [sys for sys in []]  # can be any module other than sys
    [sys.stdout.write('success\n') for _ in [1]]
f()

$ python3.11 main.py  # 3.11.9
success

$ python3.12 main.py  # 3.12.3
Traceback (most recent call last):
  File "/home/jkozera/imp/main.py", line 5, in <module>
    f()
  File "/home/jkozera/imp/main.py", line 4, in f
    [sys.stdout.write('success\n') for _ in [1]]
     ^^^
UnboundLocalError: cannot access local variable 'sys' where it is not associated with a value

$ python3.13 main.py  # 3.13.0a6+ (heads/main:2770d5c, May  2 2024, 18:19:03)
Traceback (most recent call last):
  File "/home/jkozera/imp/main.py", line 5, in <module>
    f()
    ~^^
  File "/home/jkozera/imp/main.py", line 4, in f
    [sys.stdout.write('success\n') for _ in [1]]
     ^^^
UnboundLocalError: cannot access local variable 'sys' where it is not associated with a value

CPython versions tested on:

3.11, 3.12, CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-118513: Fix sibling comprehensions with a name bound in one and global in the other #118526
• [3.12] gh-118513: Fix sibling comprehensions with a name bound in one and global in the other (GH-118526) #118548

[Eclips4]

cc @carljm

[JelleZijlstra]

Confirmed without a module too:

x = 1
def f():
    [x for x in [1]]
    return [x for _ in [1]]
print(f())

Traceback (most recent call last):
  File "/Users/jelle/py/cpython/globs.py", line 5, in <module>
    print(f())
          ~^^
  File "/Users/jelle/py/cpython/globs.py", line 4, in f
    return [x for _ in [1]]
            ^
UnboundLocalError: cannot access local variable 'x' where it is not associated with a value

Disassembly shows we're using LOAD_FAST_CHECK for the second comprehension when we should be using LOAD_GLOBAL.

[carljm]

Thanks, taking a look.

[Eclips4]

Confirmed without a module too:

x = 1
def f():
    [x for x in [1]]
    return [x for _ in [1]]
print(f())

Traceback (most recent call last):
  File "/Users/jelle/py/cpython/globs.py", line 5, in <module>
    print(f())
          ~^^
  File "/Users/jelle/py/cpython/globs.py", line 4, in f
    return [x for _ in [1]]
            ^
UnboundLocalError: cannot access local variable 'x' where it is not associated with a value

Disassembly shows we're using LOAD_FAST_CHECK for the second comprehension when we should be using LOAD_GLOBAL.

FYI, the assignment x = 1 here's unnecessary (result will be the same).

[carljm]

Yes, either way it should compile to LOAD_GLOBAL; without the global assignment it should result in NameError, not UnboundLocalError.

[carljm]

Fix in #118526