https://github.com/python/cpython/commit/46cbdf967ada11b0286060488b61635fd6a2bb23 commit: 46cbdf967ada11b0286060488b61635fd6a2bb23 branch: main author: Jelle Zijlstra <[email protected]> committer: JelleZijlstra <[email protected]> date: 2025-07-21T21:43:34-07:00 summary:
gh-135228: When @dataclass(slots=True) replaces a dataclass, make the original class collectible (#136893) An interesting hack, but more localized in scope than #135230. This may be a breaking change if people intentionally keep the original class around when using `@dataclass(slots=True)`, and then use `__dict__` or `__weakref__` on the original class. Co-authored-by: Alyssa Coghlan <[email protected]> files: A Misc/NEWS.d/next/Library/2025-07-20-16-56-55.gh-issue-135228.n_XIao.rst M Lib/dataclasses.py M Lib/test/test_dataclasses/__init__.py diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py index 83ea623dce6281..22b78bb2fbe6ed 100644 --- a/Lib/dataclasses.py +++ b/Lib/dataclasses.py @@ -1338,6 +1338,13 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields): or _update_func_cell_for__class__(member.fdel, cls, newcls)): break + # gh-135228: Make sure the original class can be garbage collected. + # Bypass mapping proxy to allow __dict__ to be removed + old_cls_dict = cls.__dict__ | _deproxier + old_cls_dict.pop('__dict__', None) + if "__weakref__" in cls.__dict__: + del cls.__weakref__ + return newcls @@ -1732,3 +1739,11 @@ def _replace(self, /, **changes): # changes that aren't fields, this will correctly raise a # TypeError. return self.__class__(**changes) + + +# Hack to the get the underlying dict out of a mappingproxy +# Use it with: cls.__dict__ | _deproxier +class _Deproxier: + def __ror__(self, other): + return other +_deproxier = _Deproxier() diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py index e98a8f284cec9f..6bf5e5b3e5554b 100644 --- a/Lib/test/test_dataclasses/__init__.py +++ b/Lib/test/test_dataclasses/__init__.py @@ -3804,6 +3804,41 @@ class WithCorrectSuper(CorrectSuper): # that we create internally. self.assertEqual(CorrectSuper.args, ["default", "default"]) + def test_original_class_is_gced(self): + # gh-135228: Make sure when we replace the class with slots=True, the original class + # gets garbage collected. + def make_simple(): + @dataclass(slots=True) + class SlotsTest: + pass + + return SlotsTest + + def make_with_annotations(): + @dataclass(slots=True) + class SlotsTest: + x: int + + return SlotsTest + + def make_with_annotations_and_method(): + @dataclass(slots=True) + class SlotsTest: + x: int + + def method(self) -> int: + return self.x + + return SlotsTest + + for make in (make_simple, make_with_annotations, make_with_annotations_and_method): + with self.subTest(make=make): + C = make() + support.gc_collect() + candidates = [cls for cls in object.__subclasses__() if cls.__name__ == 'SlotsTest' + and cls.__firstlineno__ == make.__code__.co_firstlineno + 1] + self.assertEqual(candidates, [C]) + class TestDescriptors(unittest.TestCase): def test_set_name(self): diff --git a/Misc/NEWS.d/next/Library/2025-07-20-16-56-55.gh-issue-135228.n_XIao.rst b/Misc/NEWS.d/next/Library/2025-07-20-16-56-55.gh-issue-135228.n_XIao.rst new file mode 100644 index 00000000000000..ee8962c6f46e75 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2025-07-20-16-56-55.gh-issue-135228.n_XIao.rst @@ -0,0 +1,4 @@ +When :mod:`dataclasses` replaces a class with a slotted dataclass, the +original class is now garbage collected again. Earlier changes in Python +3.14 caused this class to remain in existence together with the replacement +class synthesized by :mod:`dataclasses`. _______________________________________________ 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]
