Index: Objects/object.c
===================================================================
--- Objects/object.c	(revision 47103)
+++ Objects/object.c	(working copy)
@@ -1455,8 +1455,11 @@
 
 	if (descr == NULL) {
 		PyErr_Format(PyExc_AttributeError,
-			     "'%.100s' object has no attribute '%.200s'",
-			     tp->tp_name, PyString_AS_STRING(name));
+			     "'%.100s' object has only read-only attributes "
+			     "(%s .%.100s)",
+			     tp->tp_name,
+			     value==NULL ? "del" : "assign to",
+			     PyString_AS_STRING(name));
 		goto done;
 	}