gh-131936: Strengthen check in _suggestions._generate_suggestions

Lib/test/test_traceback.py

@@ -4619,7 +4619,31 @@ def test_levenshtein_distance_short_circuit(self):
     @cpython_only
     def test_suggestions_extension(self):
         # Check that the C extension is available
-        import _suggestions  # noqa: F401
+        import _suggestions
+
+        self.assertEqual(
+            _suggestions._generate_suggestions(
+                ["hello", "world"],
+                "hell"
+            ),
+            "hello"
+        )
+        self.assertEqual(
+            _suggestions._generate_suggestions(
+                ["hovercraft"],
+                "eels"
+            ),
+            None
+        )
+
+        # gh-131936: _generate_suggestions didn't check for exactly a list
+        class MyList(list):
+            pass
+
+        with self.assertRaises(TypeError):
+            _suggestions._generate_suggestions(MyList(), "")
+
+
 
 
 class TestColorizedTraceback(unittest.TestCase):

Modules/_suggestions.c

@@ -21,7 +21,7 @@ _suggestions__generate_suggestions_impl(PyObject *module,
 /*[clinic end generated code: output=79be7b653ae5e7ca input=ba2a8dddc654e33a]*/
 {
    // Check if dir is a list
-    if (!PyList_Check(candidates)) {
+    if (!PyList_CheckExact(candidates)) {
         PyErr_SetString(PyExc_TypeError, "candidates must be a list");
         return NULL;
     }