gh-105936: Properly update closure cells for __setattr__ and __delattr__ in frozen dataclasses with slots (GH-144021)

Lib/dataclasses.py

@@ -724,10 +724,10 @@ def _init_fn(fields, std_fields, kw_only_fields, frozen, has_post_init,
                         annotation_fields=annotation_fields)
 
 
-def _frozen_get_del_attr(cls, fields, func_builder):
-    locals = {'cls': cls,
+def _frozen_set_del_attr(cls, fields, func_builder):
+    locals = {'__class__': cls,
               'FrozenInstanceError': FrozenInstanceError}
-    condition = 'type(self) is cls'
+    condition = 'type(self) is __class__'
     if fields:
         condition += ' or name in {' + ', '.join(repr(f.name) for f in fields) + '}'
 
@@ -735,14 +735,14 @@ def _frozen_get_del_attr(cls, fields, func_builder):
                         ('self', 'name', 'value'),
                         (f'  if {condition}:',
                           '   raise FrozenInstanceError(f"cannot assign to field {name!r}")',
-                         f'  super(cls, self).__setattr__(name, value)'),
+                         f'  super(__class__, self).__setattr__(name, value)'),
                         locals=locals,
                         overwrite_error=True)
     func_builder.add_fn('__delattr__',
                         ('self', 'name'),
                         (f'  if {condition}:',
                           '   raise FrozenInstanceError(f"cannot delete field {name!r}")',
-                         f'  super(cls, self).__delattr__(name)'),
+                         f'  super(__class__, self).__delattr__(name)'),
                         locals=locals,
                         overwrite_error=True)
 
@@ -1205,7 +1205,7 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen,
                             overwrite_error='Consider using functools.total_ordering')
 
     if frozen:
-        _frozen_get_del_attr(cls, field_list, func_builder)
+        _frozen_set_del_attr(cls, field_list, func_builder)
 
     # Decide if/how we're going to create a hash function.
     hash_action = _hash_action[bool(unsafe_hash),

Lib/test/test_dataclasses/__init__.py

@@ -3052,29 +3052,41 @@ class C(base):
 
 
 class TestFrozen(unittest.TestCase):
-    def test_frozen(self):
-        @dataclass(frozen=True)
-        class C:
-            i: int
+    # Some tests have a subtest with a slotted dataclass.
+    # See https://github.com/python/cpython/issues/105936 for the reasons.
 
-        c = C(10)
-        self.assertEqual(c.i, 10)
-        with self.assertRaises(FrozenInstanceError):
-            c.i = 5
-        self.assertEqual(c.i, 10)
+    def test_frozen(self):
+        for slots in (False, True):
+            with self.subTest(slots=slots):
+
+                @dataclass(frozen=True, slots=slots)
+                class C:
+                    i: int
+
+                c = C(10)
+                self.assertEqual(c.i, 10)
+                with self.assertRaises(FrozenInstanceError):
+                    c.i = 5
+                self.assertEqual(c.i, 10)
+                with self.assertRaises(FrozenInstanceError):
+                    del c.i
+                self.assertEqual(c.i, 10)
 
     def test_frozen_empty(self):
-        @dataclass(frozen=True)
-        class C:
-            pass
+        for slots in (False, True):
+            with self.subTest(slots=slots):
 
-        c = C()
-        self.assertNotHasAttr(c, 'i')
-        with self.assertRaises(FrozenInstanceError):
-            c.i = 5
-        self.assertNotHasAttr(c, 'i')
-        with self.assertRaises(FrozenInstanceError):
-            del c.i
+                @dataclass(frozen=True, slots=slots)
+                class C:
+                    pass
+
+                c = C()
+                self.assertNotHasAttr(c, 'i')
+                with self.assertRaises(FrozenInstanceError):
+                    c.i = 5
+                self.assertNotHasAttr(c, 'i')
+                with self.assertRaises(FrozenInstanceError):
+                    del c.i
 
     def test_inherit(self):
         @dataclass(frozen=True)
@@ -3270,41 +3282,43 @@ class D(I):
                 d.i = 5
 
     def test_non_frozen_normal_derived(self):
-        # See bpo-32953.
+        # See bpo-32953 and https://github.com/python/cpython/issues/105936
+        for slots in (False, True):
+            with self.subTest(slots=slots):
 
-        @dataclass(frozen=True)
-        class D:
-            x: int
-            y: int = 10
+                @dataclass(frozen=True, slots=slots)
+                class D:
+                    x: int
+                    y: int = 10
 
-        class S(D):
-            pass
+                class S(D):
+                    pass
 
-        s = S(3)
-        self.assertEqual(s.x, 3)
-        self.assertEqual(s.y, 10)
-        s.cached = True
+                s = S(3)
+                self.assertEqual(s.x, 3)
+                self.assertEqual(s.y, 10)
+                s.cached = True
 
-        # But can't change the frozen attributes.
-        with self.assertRaises(FrozenInstanceError):
-            s.x = 5
-        with self.assertRaises(FrozenInstanceError):
-            s.y = 5
-        self.assertEqual(s.x, 3)
-        self.assertEqual(s.y, 10)
-        self.assertEqual(s.cached, True)
+                # But can't change the frozen attributes.
+                with self.assertRaises(FrozenInstanceError):
+                    s.x = 5
+                with self.assertRaises(FrozenInstanceError):
+                    s.y = 5
+                self.assertEqual(s.x, 3)
+                self.assertEqual(s.y, 10)
+                self.assertEqual(s.cached, True)
 
-        with self.assertRaises(FrozenInstanceError):
-            del s.x
-        self.assertEqual(s.x, 3)
-        with self.assertRaises(FrozenInstanceError):
-            del s.y
-        self.assertEqual(s.y, 10)
-        del s.cached
-        self.assertNotHasAttr(s, 'cached')
-        with self.assertRaises(AttributeError) as cm:
-            del s.cached
-        self.assertNotIsInstance(cm.exception, FrozenInstanceError)
+                with self.assertRaises(FrozenInstanceError):
+                    del s.x
+                self.assertEqual(s.x, 3)
+                with self.assertRaises(FrozenInstanceError):
+                    del s.y
+                self.assertEqual(s.y, 10)
+                del s.cached
+                self.assertNotHasAttr(s, 'cached')
+                with self.assertRaises(AttributeError) as cm:
+                    del s.cached
+                self.assertNotIsInstance(cm.exception, FrozenInstanceError)
 
     def test_non_frozen_normal_derived_from_empty_frozen(self):
         @dataclass(frozen=True)
@@ -3971,6 +3985,14 @@ class SlotsTest:
 
             return SlotsTest
 
+        # See https://github.com/python/cpython/issues/135228#issuecomment-3755979059
+        def make_frozen():
+            @dataclass(frozen=True, slots=True)
+            class SlotsTest:
+                pass
+
+            return SlotsTest
+
         def make_with_annotations():
             @dataclass(slots=True)
             class SlotsTest:
@@ -3996,7 +4018,7 @@ class SlotsTest:
 
             return SlotsTest
 
-        for make in (make_simple, make_with_annotations, make_with_annotations_and_method, make_with_forwardref):
+        for make in (make_simple, make_frozen, make_with_annotations, make_with_annotations_and_method, make_with_forwardref):
             with self.subTest(make=make):
                 C = make()
                 support.gc_collect()

Misc/NEWS.d/next/Library/2026-01-19-21-23-18.gh-issue-105936.dGrzjM.rst

@@ -0,0 +1,5 @@
+Attempting to mutate non-field attributes of :mod:`dataclasses`
+with both *frozen* and *slots* being ``True`` now raises
+:class:`~dataclasses.FrozenInstanceError` instead of :class:`TypeError`.
+Their non-dataclass subclasses can now freely mutate non-field attributes,
+and the original non-slotted class can be garbage collected.