pythongh-119180: Disallow instantiation of ConstEvaluator objects

JelleZijlstra · Sep 25, 2024 · 2a5a327 · 2a5a327
1 parent bc54393
commit 2a5a327
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Showing 2 changed files with 13 additions and 1 deletion.
diff --git a/Lib/test/test_type_params.py b/Lib/test/test_type_params.py
@@ -1452,3 +1452,14 @@ def f[T: (int, str)](): pass
                 self.assertEqual(annotationlib.call_evaluate_function(case.evaluate_constraints, annotationlib.Format.VALUE), (int, str))
                 self.assertEqual(annotationlib.call_evaluate_function(case.evaluate_constraints, annotationlib.Format.FORWARDREF), (int, str))
                 self.assertEqual(annotationlib.call_evaluate_function(case.evaluate_constraints, annotationlib.Format.SOURCE), '(int, str)')
+
+    def test_const_evaluator(self):
+        T = TypeVar("T", bound=int)
+        self.assertEqual(repr(T.evaluate_bound), "<constevaluator <class 'int'>>")
+
+        ConstEvaluator = type(T.evaluate_bound)
+
+        with self.assertRaisesRegex(TypeError, r"cannot create '_typing\._ConstEvaluator' instances"):
+            ConstEvaluator()
+        with self.assertRaisesRegex(TypeError, r"cannot set 'attribute' attribute of immutable type '_typing\._ConstEvaluator'"):
+            ConstEvaluator.attribute = 1
diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
@@ -242,7 +242,8 @@ static PyType_Slot constevaluator_slots[] = {
 PyType_Spec constevaluator_spec = {
     .name = "_typing._ConstEvaluator",
     .basicsize = sizeof(constevaluatorobject),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE
+        | Py_TPFLAGS_DISALLOW_INSTANTIATION,
     .slots = constevaluator_slots,
 };