From 7c936b01c4c3b2fb81c6e87481f3a4b7a1c22488 Mon Sep 17 00:00:00 2001
From: sobolevn <mail@sobolevn.me>
Date: Tue, 19 May 2026 12:44:55 +0300
Subject: [PATCH] gh-150069: Test frozen dataclass and properties interaction

---
 Lib/test/test_dataclasses/__init__.py | 71 ++++++++++++++++++++++++++-
 1 file changed, 70 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py
index 2468e3e64dd621..0e57bc4748a6bf 100644
--- a/Lib/test/test_dataclasses/__init__.py
+++ b/Lib/test/test_dataclasses/__init__.py
@@ -3328,6 +3328,47 @@ def test_non_frozen_normal_derived(self):
                 class D:
                     x: int
                     y: int = 10
+                    z: int = 0
+
+                    @property
+                    def readonly(self) -> int:
+                        return self.x
+
+                    @property
+                    def prop(self) -> int:
+                        return self.z
+
+                    @prop.setter
+                    def prop(self, val: int) -> None:
+                        object.__setattr__(self, 'z', val)
+
+                    @prop.deleter
+                    def prop(self) -> None:
+                        object.__setattr__(self, 'z', 0)
+
+                d = D(5)
+                self.assertEqual(d.x, 5)
+                self.assertEqual(d.y, 10)
+                self.assertEqual(d.z, 0)
+                self.assertEqual(d.readonly, 5)
+                self.assertEqual(d.prop, 0)
+
+                with self.assertRaises(FrozenInstanceError):
+                    d.x = 5
+                with self.assertRaises(FrozenInstanceError):
+                    d.readonly = 5
+                with self.assertRaises(FrozenInstanceError):
+                    d.z = 5
+                with self.assertRaises(FrozenInstanceError):
+                    d.prop = 5
+                with self.assertRaises(FrozenInstanceError):
+                    del d.prop
+
+                self.assertEqual(d.x, 5)
+                self.assertEqual(d.y, 10)
+                self.assertEqual(d.z, 0)
+                self.assertEqual(d.readonly, 5)
+                self.assertEqual(d.prop, 0)
 
                 class S(D):
                     pass
@@ -3335,16 +3376,35 @@ class S(D):
                 s = S(3)
                 self.assertEqual(s.x, 3)
                 self.assertEqual(s.y, 10)
+                self.assertEqual(s.z, 0)
+                self.assertEqual(s.readonly, 3)
+                self.assertEqual(s.prop, 0)
+                # Can set new attrs:
                 s.cached = True
+                # Can mutate them:
+                s.cached = False
+
+                # Can also change writable properties:
+                with self.assertRaises(AttributeError) as cm:
+                    s.readonly = 5
+                self.assertNotIsInstance(cm.exception, FrozenInstanceError)
+                s.prop = 1
+                self.assertEqual(s.x, 3)
+                self.assertEqual(s.readonly, 3)
+                self.assertEqual(s.prop, 1)
+                self.assertEqual(s.z, 1)
 
                 # But can't change the frozen attributes.
                 with self.assertRaises(FrozenInstanceError):
                     s.x = 5
                 with self.assertRaises(FrozenInstanceError):
                     s.y = 5
+                with self.assertRaises(FrozenInstanceError):
+                    s.z = 5
                 self.assertEqual(s.x, 3)
                 self.assertEqual(s.y, 10)
-                self.assertEqual(s.cached, True)
+                self.assertEqual(s.z, 1)
+                self.assertIs(s.cached, False)
 
                 with self.assertRaises(FrozenInstanceError):
                     del s.x
@@ -3352,11 +3412,20 @@ class S(D):
                 with self.assertRaises(FrozenInstanceError):
                     del s.y
                 self.assertEqual(s.y, 10)
+                with self.assertRaises(AttributeError) as cm:
+                    del s.readonly
+                self.assertNotIsInstance(cm.exception, FrozenInstanceError)
+                self.assertEqual(s.x, 3)
+                self.assertEqual(s.readonly, 3)
                 del s.cached
                 self.assertNotHasAttr(s, 'cached')
                 with self.assertRaises(AttributeError) as cm:
                     del s.cached
                 self.assertNotIsInstance(cm.exception, FrozenInstanceError)
+                del s.prop
+                self.assertEqual(s.z, 0)
+                self.assertEqual(s.prop, 0)
+                del s.prop
 
     def test_non_frozen_normal_derived_from_empty_frozen(self):
         @dataclass(frozen=True)