Issue #28790: Fix error when using Generic and __slots__ (Ivan L)

Lib/test/test_typing.py

@@ -896,6 +896,44 @@ class GenericTests(BaseTestCase):
             self.assertEqual(t, copy(t))
             self.assertEqual(t, deepcopy(t))
 
+    def test_parameterized_slots(self):
+        T = TypeVar('T')
+        class C(Generic[T]):
+            __slots__ = ('potato',)
+
+        c = C()
+        c_int = C[int]()
+        self.assertEqual(C.__slots__, C[str].__slots__)
+
+        c.potato = 0
+        c_int.potato = 0
+        with self.assertRaises(AttributeError):
+            c.tomato = 0
+        with self.assertRaises(AttributeError):
+            c_int.tomato = 0
+
+        def foo(x: C['C']): ...
+        self.assertEqual(get_type_hints(foo, globals(), locals())['x'], C[C])
+        self.assertEqual(get_type_hints(foo, globals(), locals())['x'].__slots__,
+                         C.__slots__)
+        self.assertEqual(copy(C[int]), deepcopy(C[int]))
+
+    def test_parameterized_slots_dict(self):
+        T = TypeVar('T')
+        class D(Generic[T]):
+            __slots__ = {'banana': 42}
+
+        d = D()
+        d_int = D[int]()
+        self.assertEqual(D.__slots__, D[str].__slots__)
+
+        d.banana = 'yes'
+        d_int.banana = 'yes'
+        with self.assertRaises(AttributeError):
+            d.foobar = 'no'
+        with self.assertRaises(AttributeError):
+            d_int.foobar = 'no'
+
     def test_errors(self):
         with self.assertRaises(TypeError):
             B = SimpleMapping[XK, Any]