Add PyDict_Merge(a, b, override):

PyDict_Merge(a, b, 1) is the same as PyDict_Update(a, b).
PyDict_Merge(a, b, 0) does something similar but leaves existing items
unchanged.

diff --git a/Include/dictobject.h b/Include/dictobject.h
index abc8ed567d0c5631b13ae2bd1a5870cd27d95d4f..11320214e990e7c4becb9a1be3a059c0d07d2cee 100644 (file)
--- a/Include/dictobject.h
+++ b/Include/dictobject.h
@@ -98,6 +98,7 @@ extern DL_IMPORT(PyObject *) PyDict_Items(PyObject *mp);
 extern DL_IMPORT(int) PyDict_Size(PyObject *mp);
 extern DL_IMPORT(PyObject *) PyDict_Copy(PyObject *mp);
 extern DL_IMPORT(int) PyDict_Update(PyObject *mp, PyObject *other);
+extern DL_IMPORT(int) PyDict_Merge(PyObject *mp, PyObject *other, int override);
 
 
 extern DL_IMPORT(PyObject *) PyDict_GetItemString(PyObject *dp, char *key);

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index ce4c578f421c1b11f3a7bfffc707ec4e63adbc56..73c459fb41ce359cbed2a8248b7794d9151b28ea 100644 (file)
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -999,8 +999,18 @@ dict_update(PyObject *mp, PyObject *args)
        return Py_None;
 }
 
+/* Update unconditionally replaces existing items.
+   Merge has a 3rd argument 'override'; if set, it acts like Update,
+   otherwise it leaves existing items unchanged. */
+
 int
 PyDict_Update(PyObject *a, PyObject *b)
+{
+       return PyDict_Merge(a, b, 1);
+}
+
+int
+PyDict_Merge(PyObject *a, PyObject *b, int override)
 {
        register PyDictObject *mp, *other;
        register int i;
@@ -1031,7 +1041,9 @@ PyDict_Update(PyObject *a, PyObject *b)
                }
                for (i = 0; i <= other->ma_mask; i++) {
                        entry = &other->ma_table[i];
-                       if (entry->me_value != NULL) {
+                       if (entry->me_value != NULL &&
+                           (override ||
+                            PyDict_GetItem(a, entry->me_key) == NULL)) {
                                Py_INCREF(entry->me_key);
                                Py_INCREF(entry->me_value);
                                insertdict(mp, entry->me_key, entry->me_hash,
@@ -1060,13 +1072,17 @@ PyDict_Update(PyObject *a, PyObject *b)
                        return -1;
 
                for (key = PyIter_Next(iter); key; key = PyIter_Next(iter)) {
+                       if (!override && PyDict_GetItem(a, key) != NULL) {
+                               Py_DECREF(key);
+                               continue;
+                       }
                        value = PyObject_GetItem(b, key);
                        if (value == NULL) {
                                Py_DECREF(iter);
                                Py_DECREF(key);
                                return -1;
                        }
-                       status = PyDict_SetItem((PyObject*)mp, key, value);
+                       status = PyDict_SetItem(a, key, value);
                        Py_DECREF(key);
                        Py_DECREF(value);
                        if (status < 0) {