Changed networkx import line; we may have to deal with version issues here.

mininet/topo.py

@@ -11,7 +11,11 @@
 setup for testing, and can even be emulated with the Mininet package.
 '''
 
-from networkx.classes.graph import Graph
+# BL: we may have to fix compatibility here.
+# networkx is also a fairly heavyweight dependency
+# from networkx.classes.graph import Graph
+
+from networkx import Graph
 from mininet.node import SWITCH_PORT_BASE
 
 class NodeID(object):