Index: Objects/abstract.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Objects/abstract.c,v
retrieving revision 2.139
diff -u -p -r2.139 abstract.c
--- Objects/abstract.c	24 Sep 2005 21:23:05 -0000	2.139
+++ Objects/abstract.c	28 Sep 2005 12:17:24 -0000
@@ -1277,6 +1277,7 @@ int
 PySequence_SetItem(PyObject *s, int i, PyObject *o)
 {
 	PySequenceMethods *m;
+	PyObject *item;
 
 	if (s == NULL) {
 		null_error();
@@ -1295,6 +1296,19 @@ PySequence_SetItem(PyObject *s, int i, P
 		}
 		return m->sq_ass_item(s, i, o);
 	}
+	
+	/* before erroring out, check if the item we want to assign
+	 * is already at the specified index; this makes it possible
+	 * to use inplace operators on mutable types inside immutable
+	 * containers */
+	
+	item = PySequence_GetItem(s, i);
+	if (item && item == o) {
+		Py_DECREF(item);
+		return 0;
+	}
+	Py_XDECREF(item);
+		
 
 	type_error("object does not support item assignment");
 	return -1;