# HG changeset patch
# Parent 154d6335a2c66b35a268c31fb24d183be661d896
add PyDict_SetItemDefault() C-API function to implement dict.setdefault() at the C-API level

diff -r 154d6335a2c6 Doc/c-api/dict.rst
--- a/Doc/c-api/dict.rst	Thu Mar 07 14:03:27 2013 +0100
+++ b/Doc/c-api/dict.rst	Thu Mar 07 15:03:03 2013 +0100
@@ -110,6 +110,16 @@
    :c:type:`char\*`, rather than a :c:type:`PyObject\*`.
 
 
+.. c:function:: PyObject* PyDict_GetItemSetDefault(PyObject *p, PyObject *key, PyObject *default)
+
+   Read the value with a key of *key* from the dictionary *p*.  If the key is
+   not in the dict, insert it with value *defaultobj* and return *defaultobj*.
+   This function evaluates the hash function of *key* only once, instead of
+   evaluating it independently for the lookup and the insertion.  *key* must
+   be :term:`hashable`; if it isn't, :exc:`TypeError` will be raised.  This
+   is the same as ``p.setdefault(key, default)`` in Python.
+
+
 .. c:function:: PyObject* PyDict_Items(PyObject *p)
 
    Return a :c:type:`PyListObject` containing all the items from the dictionary.
diff -r 154d6335a2c6 Doc/data/refcounts.dat
--- a/Doc/data/refcounts.dat	Thu Mar 07 14:03:27 2013 +0100
+++ b/Doc/data/refcounts.dat	Thu Mar 07 15:03:03 2013 +0100
@@ -220,6 +220,11 @@
 PyDict_GetItemString:PyObject*:p:0:
 PyDict_GetItemString:char*:key::
 
+PyDict_GetItemSetDefault:PyObject*::0:
+PyDict_GetItemSetDefault:PyObject*:p:0:
+PyDict_GetItemSetDefault:PyObject*:key:0:conditionally +1 if inserted into the dict
+PyDict_GetItemSetDefault:PyObject*:default:0:conditionally +1 if inserted into the dict
+
 PyDict_Items:PyObject*::+1:
 PyDict_Items:PyObject*:p:0:
 
diff -r 154d6335a2c6 Include/dictobject.h
--- a/Include/dictobject.h	Thu Mar 07 14:03:27 2013 +0100
+++ b/Include/dictobject.h	Thu Mar 07 15:03:03 2013 +0100
@@ -53,6 +53,8 @@
 PyAPI_FUNC(PyObject *) PyDict_GetItemWithError(PyObject *mp, PyObject *key);
 PyAPI_FUNC(PyObject *) _PyDict_GetItemIdWithError(PyObject *dp,
                                                   struct _Py_Identifier *key);
+PyAPI_FUNC(PyObject *) PyDict_GetItemSetDefault(
+    PyObject *mp, PyObject *key, PyObject *defaultobj);
 PyAPI_FUNC(int) PyDict_SetItem(PyObject *mp, PyObject *key, PyObject *item);
 PyAPI_FUNC(int) PyDict_DelItem(PyObject *mp, PyObject *key);
 PyAPI_FUNC(void) PyDict_Clear(PyObject *mp);
diff -r 154d6335a2c6 Objects/dictobject.c
--- a/Objects/dictobject.c	Thu Mar 07 14:03:27 2013 +0100
+++ b/Objects/dictobject.c	Thu Mar 07 15:03:03 2013 +0100
@@ -2211,19 +2211,41 @@
     return val;
 }
 
+static PyObject* dict_getitemsetdefault(
+    PyDictObject *d, PyObject *key, PyObject *defaultobj);
+
+PyObject*
+PyDict_GetItemSetDefault(PyObject *d, PyObject *key, PyObject *defaultobj)
+{
+    if ((key == NULL | defaultobj == NULL | d == NULL) || !PyDict_Check(d)) {
+        PyErr_BadInternalCall();
+        return NULL;
+    }
+    return dict_getitemsetdefault((PyDictObject*) d, key, defaultobj);
+}
+
 static PyObject *
-dict_setdefault(register PyDictObject *mp, PyObject *args)
+dict_setdefault(PyDictObject *mp, PyObject *args)
 {
-    PyObject *key;
-    PyObject *failobj = Py_None;
+    PyObject *key, *val;
+    PyObject *defaultobj = Py_None;
+
+    if (!PyArg_UnpackTuple(args, "setdefault", 1, 2, &key, &defaultobj))
+        return NULL;
+
+    val = dict_getitemsetdefault(mp, key, defaultobj);
+    Py_XINCREF(val);
+    return val;
+}
+
+static PyObject*
+dict_getitemsetdefault(PyDictObject *mp, PyObject *key, PyObject *defaultobj)
+{
     PyObject *val = NULL;
     Py_hash_t hash;
     PyDictKeyEntry *ep;
     PyObject **value_addr;
 
-    if (!PyArg_UnpackTuple(args, "setdefault", 1, 2, &key, &failobj))
-        return NULL;
-
     if (!PyUnicode_CheckExact(key) ||
         (hash = ((PyASCIIObject *) key)->hash) == -1) {
         hash = PyObject_Hash(key);
@@ -2241,17 +2263,16 @@
                 return NULL;
             ep = find_empty_slot(mp, key, hash, &value_addr);
         }
-        Py_INCREF(failobj);
+        Py_INCREF(defaultobj);
         Py_INCREF(key);
-        MAINTAIN_TRACKING(mp, key, failobj);
+        MAINTAIN_TRACKING(mp, key, defaultobj);
         ep->me_key = key;
         ep->me_hash = hash;
-        *value_addr = failobj;
-        val = failobj;
+        *value_addr = defaultobj;
+        val = defaultobj;
         mp->ma_keys->dk_usable--;
         mp->ma_used++;
     }
-    Py_INCREF(val);
     return val;
 }