diff -r b622e411eef8 tools/python/xen/xend/sxp.py
--- a/tools/python/xen/xend/sxp.py	Thu Jun 24 21:56:03 2010 +0100
+++ b/tools/python/xen/xend/sxp.py	Mon Jun 28 14:09:33 2010 +0800
@@ -365,6 +365,8 @@
 def atomp(sxpr):
     """Check if an sxpr is an atom.
     """
+    if sxpr == '':
+        return 0
     if sxpr.isalnum() or sxpr == '@':
         return 1
     for c in sxpr: