Fix is_switch() to always succeed + whitespace edits.

mininet/topo.py

@@ -16,7 +16,7 @@ setup for testing, and can even be emulated with the Mininet package.
 # from networkx.classes.graph import Graph
 
 from networkx import Graph
-from mininet.util import netParse, ipStr, irange, natural, naturalSeq
+from mininet.util import irange, natural, naturalSeq
 
 class Topo(object):
     "Data center network representation for structured multi-trees."
@@ -113,7 +113,7 @@ class Topo(object):
     def is_switch(self, n):
         '''Returns true if node is a switch.'''
         info = self.node_info[n]
-        return info and info['is_switch']
+        return info and info.get('is_switch', False)
 
     def switches(self, sort=True):
         '''Return switches.
@@ -163,6 +163,7 @@ class Topo(object):
         return info if info is not None else {}
 
     def setNodeInfo( self, name, info ):
+        "Set metadata (dict) for node"
         self.node_info[ name ] = info
 
     @staticmethod