diff -r 0bf6c52447d0 -r 4e76477949d5 entity.py
--- a/entity.py	Tue Aug 25 23:29:05 2009 +0200
+++ b/entity.py	Tue Aug 25 23:34:30 2009 +0200
@@ -315,6 +315,9 @@
     def __hash__(self):
         return id(self)
 
+    def __cmp__(self):
+        raise NotImplementedError('comparison not implemented for %s' % self.__class__)
+
     def pre_add_hook(self):
         """hook called by the repository before doing anything to add the entity
         (before_add entity hooks have not been called yet). This give the