diff -r a957182a866f src/obengine/datatypes.py
--- a/src/obengine/datatypes.py Fri Aug 24 11:58:06 2012 -0500
+++ b/src/obengine/datatypes.py Fri Nov 02 15:18:09 2012 -0500
@@ -26,7 +26,10 @@
 __date__ = "$May 4, 2011 8:08:03 PM$"


-import collections
+try:
+    from collections import MutableSet
+except AttributeError:
+    from sets import Set as MutableSet
 import heapq

 import obengine.event
@@ -155,7 +158,7 @@
         self._extensions[name] = extension


-class orderedset(collections.MutableSet):
+class orderedset(MutableSet):
     """Ordered set - like a set, but remembers insertion order
     Based on Raymond Hettinger's ASPN recipe (
     http://code.activestate.com/recipes/576694/).
@@ -257,7 +260,7 @@
         self.clear()


-class heap(collections.Sequence):
+class heap(object):
     """OO wrapper around the standard heapq module
     This class provides an object-oriented wrapper around the
     standard heapq module.