regressing the performance bugfix -- Guido wants the performance bug left

alone, because there can be no guarantee re the semantics of += vs + .

Misc/NEWS

@@ -47,9 +47,6 @@ Core and builtins
 - obj.__contains__() now returns True/False instead of 1/0.  SF patch
   820195.
 
-- builtin_sum() now uses PyNumber_InPlaceAdd, fixing a previous
-  performance bug for sum(list_of_lists) and similar cases.
-
 Extension modules
 -----------------
 

Python/bltinmodule.c

@@ -1840,7 +1840,7 @@ builtin_sum(PyObject *self, PyObject *args)
 			}
 			break;
 		}
-		temp = PyNumber_InPlaceAdd(result, item);
+		temp = PyNumber_Add(result, item);
 		Py_DECREF(result);
 		Py_DECREF(item);
 		result = temp;