gh-129573: Fix possible abort from non-string suggestions in calculate_suggestions/_Py_CalculateSuggestions

Lib/test/test_traceback.py

@@ -4072,6 +4072,14 @@ class A:
         actual = self.get_suggestion(A(), 'bluch')
         self.assertNotIn("blech", actual)
 
+    def test_suggestions_do_not_trigger_with_non_string_candidates(self):
+        def run_module_code():
+            import runpy
+            runpy._run_module_code("blech", {0: "", "bluch": ""}, "")
+
+        actual = self.get_exception(run_module_code, slice_start=-1, slice_end=None)
+        self.assertNotIn("bluch", actual[0])
+
     def test_getattr_suggestions_no_args(self):
         class A:
             blech = None

Python/suggestions.c

@@ -148,6 +148,10 @@ _Py_CalculateSuggestions(PyObject *dir,
     }
     for (Py_ssize_t i = 0; i < dir_size; ++i) {
         PyObject *item = PyList_GET_ITEM(dir, i);
+        if (!PyUnicode_Check(item)) {
+            PyMem_Free(buffer);
+            return NULL;
+        }
         if (_PyUnicode_Equal(name, item)) {
             continue;
         }