Bug report

Bug description:

Name mangling behaves inconsistently when used with generics. Here’s the code to reproduce the issue:

class __Foo(type):
    pass


class Bar[T](metaclass=__Foo):
    pass

This raises NameError: name '_Bar__Foo' is not defined. However, removing the [T] results in the error disappearing. This suggests that the name mangling behavior is inconsistent when generics are involved. This behavior seems to be a bug, as it would be expected for the name mangling to either always occur or never occur, regardless of whether generics are used.

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

• gh-119311: Fix name mangling with PEP 695 generic classes #119464
• [3.13] gh-119311: Fix name mangling with PEP 695 generic classes (#119464) #119643
• [3.12] gh-119311: Fix name mangling with PEP 695 generic classes (#119464) #119644
• gh-119311: Add missing magic number (3571) for 3.13.0b1 #125771