[3.13] pythongh-135878: Fix crash in types.SimpleNamespace.__repr__ (pythonGH-135889) (python#135895)

pythongh-135878: Fix crash in `types.SimpleNamespace.__repr__` (pythonGH-135889)
(cherry picked from commit b3ab94a)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

Author: 3 people

Misc/NEWS.d/next/Library/2025-06-24-14-43-24.gh-issue-135878.Db4roX.rst

@@ -0,0 +1,3 @@
+Fixes a crash of :class:`types.SimpleNamespace` on :term:`free threading` builds,
+when several threads were calling its :meth:`~object.__repr__` method at the
+same time.

Objects/namespaceobject.c

@@ -120,9 +120,10 @@ namespace_repr(PyObject *ns)
         if (PyUnicode_Check(key) && PyUnicode_GET_LENGTH(key) > 0) {
             PyObject *value, *item;
 
-            value = PyDict_GetItemWithError(d, key);
-            if (value != NULL) {
+            int has_key = PyDict_GetItemRef(d, key, &value);
+            if (has_key == 1) {
                 item = PyUnicode_FromFormat("%U=%R", key, value);
+                Py_DECREF(value);
                 if (item == NULL) {
                     loop_error = 1;
                 }
@@ -131,7 +132,7 @@ namespace_repr(PyObject *ns)
                     Py_DECREF(item);
                 }
             }
-            else if (PyErr_Occurred()) {
+            else if (has_key < 0) {
                 loop_error = 1;
             }
         }