gh-119494: Fix error messages for deleting/setting type attributes (#119495)

Author: da-woods

Lib/test/test_descr.py

@@ -4078,7 +4078,7 @@ class E(D):
         self.assertEqual(C2.__subclasses__(), [D])
 
         with self.assertRaisesRegex(TypeError,
-                    "cannot delete '__bases__' attribute of immutable type"):
+                    "cannot delete '__bases__' attribute of type 'D'"):
             del D.__bases__
         with self.assertRaisesRegex(TypeError, 'can only assign non-empty tuple'):
             D.__bases__ = ()
@@ -5062,7 +5062,7 @@ class X:
 
         with self.assertRaises(TypeError) as cm:
             type(X).__dict__["__doc__"].__delete__(X)
-        self.assertIn("cannot delete '__doc__' attribute of immutable type 'X'", str(cm.exception))
+        self.assertIn("cannot delete '__doc__' attribute of type 'X'", str(cm.exception))
         self.assertEqual(X.__doc__, "banana")
 
     def test_qualname(self):

Misc/NEWS.d/next/Core_and_Builtins/2024-05-24-07-02-47.gh-issue-119494.x3KUMC.rst

@@ -0,0 +1 @@
+Exception text when trying to delete attributes of types was clarified.

Objects/typeobject.c

@@ -1465,15 +1465,15 @@ static PyMemberDef type_members[] = {
 static int
 check_set_special_type_attr(PyTypeObject *type, PyObject *value, const char *name)
 {
-    if (_PyType_HasFeature(type, Py_TPFLAGS_IMMUTABLETYPE)) {
+    if (!value) {
         PyErr_Format(PyExc_TypeError,
-                     "cannot set '%s' attribute of immutable type '%s'",
+                     "cannot delete '%s' attribute of type '%s'",
                      name, type->tp_name);
         return 0;
     }
-    if (!value) {
+    if (_PyType_HasFeature(type, Py_TPFLAGS_IMMUTABLETYPE)) {
         PyErr_Format(PyExc_TypeError,
-                     "cannot delete '%s' attribute of immutable type '%s'",
+                     "cannot set '%s' attribute of immutable type '%s'",
                      name, type->tp_name);
         return 0;
     }