pythongh-118895: Call PyType_Ready() on typing.NoDefault

Include/internal/pycore_typevarobject.h

@@ -18,6 +18,7 @@ extern int _Py_initialize_generic(PyInterpreterState *);
 extern void _Py_clear_generic_types(PyInterpreterState *);
 
 extern PyTypeObject _PyTypeAlias_Type;
+extern PyTypeObject _PyNoDefault_Type;
 extern PyObject _Py_NoDefaultStruct;
 
 #ifdef __cplusplus

Lib/test/test_typing.py

@@ -10236,7 +10236,7 @@ def test_pickling(self):
     def test_constructor(self):
         self.assertIs(NoDefault, type(NoDefault)())
         with self.assertRaises(TypeError):
-            NoDefault(1)
+            type(NoDefault)(1)
 
     def test_repr(self):
         self.assertEqual(repr(NoDefault), 'typing.NoDefault')
@@ -10245,6 +10245,16 @@ def test_no_call(self):
         with self.assertRaises(TypeError):
             NoDefault()
 
+    def test_no_attributes(self):
+        with self.assertRaises(AttributeError):
+            NoDefault.foo = 3
+        with self.assertRaises(AttributeError):
+            NoDefault.foo
+
+        # TypeError is consistent with the behavior of NoneType
+        with self.assertRaises(TypeError):
+            type(NoDefault).foo = 3
+
 
 class AllTests(BaseTestCase):
     """Tests for __all__."""

Misc/NEWS.d/next/Library/2024-05-10-05-24-32.gh-issue-118895.wUm5r2.rst

@@ -0,0 +1,2 @@
+Setting attributes on :data:`typing.NoDefault` now raises
+:exc:`AttributeError` instead of :exc:`TypeError`.

Modules/_typingmodule.c

@@ -63,6 +63,9 @@ _typing_exec(PyObject *m)
     if (PyModule_AddObjectRef(m, "TypeAliasType", (PyObject *)&_PyTypeAlias_Type) < 0) {
         return -1;
     }
+    if (PyType_Ready(&_PyNoDefault_Type) < 0) {
+        return -1;
+    }
     if (PyModule_AddObjectRef(m, "NoDefault", (PyObject *)&_Py_NoDefaultStruct) < 0) {
         return -1;
     }