https://github.com/python/cpython/commit/6d7bbee1d5714a345dca5a7e4089de3c2fc0fb59 commit: 6d7bbee1d5714a345dca5a7e4089de3c2fc0fb59 branch: main author: Jelle Zijlstra <[email protected]> committer: JelleZijlstra <[email protected]> date: 2026-04-25T08:31:22-07:00 summary:
gh-148947: dataclasses: fix error on empty __class__ cell (#148948) Also add a test demonstrating the need for the existing "is oldcls" check. Co-authored-by: Bartosz Sławecki <[email protected]> files: A Misc/NEWS.d/next/Library/2026-04-23-21-47-49.gh-issue-148947.W4V2lG.rst M Lib/dataclasses.py M Lib/test/test_dataclasses/__init__.py diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py index 9d5bed6b96fc49..988edfed6f4dcb 100644 --- a/Lib/dataclasses.py +++ b/Lib/dataclasses.py @@ -1298,10 +1298,18 @@ def _update_func_cell_for__class__(f, oldcls, newcls): # This function doesn't reference __class__, so nothing to do. return False # Fix the cell to point to the new class, if it's already pointing - # at the old class. I'm not convinced that the "is oldcls" test - # is needed, but other than performance can't hurt. + # at the old class. closure = f.__closure__[idx] - if closure.cell_contents is oldcls: + + try: + contents = closure.cell_contents + except ValueError: + # Cell is empty + return False + + # This check makes it so we avoid updating an incorrect cell if the + # class body contains a function that was defined in a different class. + if contents is oldcls: closure.cell_contents = newcls return True return False diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py index e0cfe3df3e6357..6ff82b8810abed 100644 --- a/Lib/test/test_dataclasses/__init__.py +++ b/Lib/test/test_dataclasses/__init__.py @@ -5375,5 +5375,51 @@ def cls(self): # one will be keeping a reference to the underlying class A. self.assertIs(A().cls(), B) + def test_empty_class_cell(self): + # gh-148947: Make sure that we explicitly handle the empty class cell. + def maker(): + if False: + __class__ = 42 + + def method(self): + return __class__ + return method + + from dataclasses import dataclass + + @dataclass(slots=True) + class X: + a: int + + meth = maker() + + with self.assertRaisesRegex(NameError, '__class__'): + X(1).meth() + + def test_class_cell_from_other_class(self): + # This test fails without the "is oldcls" check in + # _update_func_cell_for__class__. + class Base: + def meth(self): + return "Base" + + class Child(Base): + def meth(self): + return super().meth() + " Child" + + @dataclass(slots=True) + class DC(Child): + a: int + + meth = Child.meth + + closure = DC.meth.__closure__ + self.assertEqual(len(closure), 1) + self.assertIs(closure[0].cell_contents, Child) + + self.assertEqual(DC(1).meth(), "Base Child") + + + if __name__ == '__main__': unittest.main() diff --git a/Misc/NEWS.d/next/Library/2026-04-23-21-47-49.gh-issue-148947.W4V2lG.rst b/Misc/NEWS.d/next/Library/2026-04-23-21-47-49.gh-issue-148947.W4V2lG.rst new file mode 100644 index 00000000000000..f9783266f5cc42 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-04-23-21-47-49.gh-issue-148947.W4V2lG.rst @@ -0,0 +1,2 @@ +Fix crash in :deco:`dataclasses.dataclass` with ``slots=True`` that occurred +when a function found within the class had an empty ``__class__`` cell. _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
