Description

JelleZijlstra

opened on May 11, 2023

Issue body actions

Code:

class X:
    y = 1
    print([x + y for x in range(3)])

On current main:

Python 3.12.0a7+ (heads/main:94f30c7557, May 10 2023, 17:27:39) [Clang 14.0.0 (clang-1400.0.29.202)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> class X:
...     y = 1
...     print([x + y for x in range(3)])
... 
[1, 2, 3]

But on 3.11:

>>> class X:
...     y = 1
...     print([x + y for x in range(3)])
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in X
  File "<stdin>", line 3, in <listcomp>
NameError: name 'y' is not defined

I actually like the new behavior, and I discovered this bug as I was preparing a post proposing that we make things work this way in 3.13. But it's a behavior change, and we should only make this change on purpose and not by accident.

This could plausibly break real code if the name is defined in both the module and class scope, and current code relies on getting the name from the module scope.

cc @carljm

Linked PRs

• gh-104374: don't inline comprehensions in non-function scopes #104519
• gh-104374: Remove access to class scopes for inlined comprehensions #104528

Activity

1. JelleZijlstra

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   release-blocker

   on May 11, 2023
2. ezio-melotti

   added this to Release and Deferred blockers 🚫on May 11, 2023
3. github-project-automation

   moved this to Todo in Release and Deferred blockers 🚫on May 11, 2023
4. JelleZijlstra

   changed the title [-]List comprehension now have access to the enclosing class scope[/-] [+]List comprehensions now have access to the enclosing class scope[/+] on May 11, 2023
5. asishm-wk commented on May 11, 2023

   

   asishm-wk

   on May 11, 2023

   More actions

   on 3.10.8 - this prints [1,2,3]
6. JelleZijlstra commented on May 11, 2023

   

   JelleZijlstra

   on May 11, 2023

   MemberAuthor

   More actions

   I don't think so. I just confirmed on 3.10.9 (don't have a 3.10.8 around), and it throws a NameError. Make sure you run the sample in a class scope.
7. asishm-wk commented on May 11, 2023

   

   asishm-wk

   on May 11, 2023

   More actions

   sorry, you're right! - I forgot to restart the interpreter when testing different variations - so there was already a y defined in the outer scope!
8. carljm commented on May 11, 2023

   

   carljm

   on May 11, 2023

   Member

   More actions

   I started a Discourse thread about options for handling this: https://discuss.python.org/t/pep-709-one-behavior-change-that-was-missed-in-the-pep/26691
9. carljm commented on May 13, 2023

   

   carljm

   on May 13, 2023

   Member

   More actions

   I filed a SC issue about this: python/steering-council#189
10. carljm

    added a commit that references this issue on May 16, 2023

    pythongh-104374: don't inline comprehensions in non-function scopes

    9d452fb
11. JelleZijlstra

    added 2 commits that reference this issue on May 16, 2023

    pythongh-104374: Remove access to class scopes for inlined comprehens…

    3fad7b0

    gh-104374: Remove access to class scopes for inlined comprehensions (#…

    662aede
12. carljm

    closed this as completedon May 18, 2023
13. github-project-automation

    moved this from Todo to Done in Release and Deferred blockers 🚫on May 18, 2023

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