Add PyDict_SetDefaultRef()

Author: vstinner

pythoncapi_compat.h

@@ -1298,6 +1298,47 @@ PyList_GetItemRef(PyObject *op, Py_ssize_t index)
 #endif
 
 
+// gh-114329 added PyList_GetItemRef() to Python 3.13.0a4
+#if PY_VERSION_HEX < 0x030D00A4
+static int
+PyDict_SetDefaultRef(PyObject *d, PyObject *key, PyObject *default_value,
+                     PyObject **result)
+{
+    PyObject *value;
+    if (PyDict_GetItemRef(d, key, &value) < 0) {
+        // get error
+        if (result) {
+            *result = NULL;
+        }
+        return -1;
+    }
+    if (value != NULL) {
+        // present
+        if (result) {
+            *result = value;
+        }
+        else {
+            Py_DECREF(value);
+        }
+        return 1;
+    }
+
+    // missing: set the item
+    if (PyDict_SetItem(d, key, default_value) < 0) {
+        // set error
+        if (result) {
+            *result = NULL;
+        }
+        return -1;
+    }
+    if (result) {
+        *result = Py_NewRef(default_value);
+    }
+    return 0;
+}
+#endif
+
+
 #ifdef __cplusplus
 }
 #endif

tests/test_pythoncapi_compat_cext.c

@@ -1329,6 +1329,62 @@ test_dict_pop(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
 }
 
 
+static PyObject *
+test_dict_setdefault(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
+{
+    PyObject *dict = PyDict_New();
+    if (dict == NULL) {
+        return NULL;
+    }
+    PyObject *key = PyUnicode_FromString("key");
+    assert(key != NULL);
+    PyObject *value = PyUnicode_FromString("abc");
+    assert(value != NULL);
+    PyObject *invalid_key = PyList_New(0);  // not hashable key
+    assert(invalid_key != NULL);
+
+    // insert item
+    PyObject *result = UNINITIALIZED_OBJ;
+    assert(PyDict_SetDefaultRef(dict, key, value, &result) == 0);
+    assert(result == value);
+    Py_DECREF(result);
+
+    // item already present
+    result = UNINITIALIZED_OBJ;
+    assert(PyDict_SetDefaultRef(dict, key, value, &result) == 1);
+    assert(result == value);
+    Py_DECREF(result);
+
+    // error: invalid key
+    assert(!PyErr_Occurred());
+    result = UNINITIALIZED_OBJ;
+    assert(PyDict_SetDefaultRef(dict, invalid_key, value, &result) == -1);
+    assert(result == NULL);
+    assert(PyErr_Occurred());
+    PyErr_Clear();
+
+    // insert item with NULL result
+    assert(PyDict_Pop(dict, key, NULL) == 1);
+    assert(PyDict_SetDefaultRef(dict, key, value, NULL) == 0);
+
+    // item already present with NULL result
+    assert(PyDict_SetDefaultRef(dict, key, value, NULL) == 1);
+
+    // error: invalid key with NULL result
+    assert(!PyErr_Occurred());
+    assert(PyDict_SetDefaultRef(dict, invalid_key, value, NULL) == -1);
+    assert(PyErr_Occurred());
+    PyErr_Clear();
+
+    // exit
+    Py_DECREF(dict);
+    Py_DECREF(key);
+    Py_DECREF(value);
+    Py_DECREF(invalid_key);
+    Py_RETURN_NONE;
+}
+
+
 static PyObject *
 test_long_api(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
 {
@@ -1694,6 +1750,7 @@ static struct PyMethodDef methods[] = {
     {"test_getitem", test_getitem, METH_NOARGS, _Py_NULL},
     {"test_dict_api", test_dict_api, METH_NOARGS, _Py_NULL},
     {"test_dict_pop", test_dict_pop, METH_NOARGS, _Py_NULL},
+    {"test_dict_setdefault", test_dict_setdefault, METH_NOARGS, _Py_NULL},
     {"test_long_api", test_long_api, METH_NOARGS, _Py_NULL},
 #ifdef TEST_MANAGED_DICT
     {"test_managed_dict", test_managed_dict, METH_NOARGS, _Py_NULL},