old_contents: """Custom topology example
  
  author: Brandon Heller (brandonh@stanford.edu)
  
  Two directly connected switches plus a host for each switch:
  
     host --- switch --- switch --- host
  
  Adding the 'topos' dict with a key/value pair to generate our newly defined
  topology enables one to pass in '--topo=mytopo' from the command line.
  """
  
  from mininet.topo import Topo, Node
  
  class MyTopo( Topo ):
      "Simple topology example."
  
      def __init__( self, enable_all = True ):
          "Create custom topo."
  
          # Add default members to class.
          super( MyTopo, self ).__init__()
  
          # Set Node IDs for hosts and switches
          leftHost = 1
          leftSwitch = 2
          rightSwitch = 3
          rightHost = 4
  
          # Add nodes
          self.addNode( leftSwitch, Node( isSwitch=True ) )
          self.addNode( rightSwitch, Node( isSwitch=True ) )
          self.addNode( leftHost, Node( isSwitch=False ) )
          self.addNode( rightHost, Node( isSwitch=False ) )
  
          # Add edges
          self.add_edge( leftHost, leftSwitch )
          self.add_edge( leftSwitch, rightSwitch )
          self.add_edge( rightSwitch, rightHost )
  
          # Consider all switches and hosts 'on'
          self.enable_all()
  
  
  topos = { 'mytopo': ( lambda: MyTopo() ) }
  
new_contents: """Custom topology example
  
  author: Brandon Heller (brandonh@stanford.edu)
  
  Two directly connected switches plus a host for each switch:
  
     host --- switch --- switch --- host
  
  Adding the 'topos' dict with a key/value pair to generate our newly defined
  topology enables one to pass in '--topo=mytopo' from the command line.
  """
  
  from mininet.topo import Topo
  from mininet.node import Node
  
  class MyTopo( Topo ):
      "Simple topology example."
  
      def __init__( self, enable_all = True ):
          "Create custom topo."
  
          # Add default members to class.
          super( MyTopo, self ).__init__()
  
          # Set Node IDs for hosts and switches
          leftHost = 1
          leftSwitch = 2
          rightSwitch = 3
          rightHost = 4
  
          # Add nodes
          self.addNode( leftSwitch, Node( isSwitch=True ) )
          self.addNode( rightSwitch, Node( isSwitch=True ) )
          self.addNode( leftHost, Node( isSwitch=False ) )
          self.addNode( rightHost, Node( isSwitch=False ) )
  
          # Add edges
          self.add_edge( leftHost, leftSwitch )
          self.add_edge( leftSwitch, rightSwitch )
          self.add_edge( rightSwitch, rightHost )
  
          # Consider all switches and hosts 'on'
          self.enable_all()
  
  
  topos = { 'mytopo': ( lambda: MyTopo() ) }
  
subject: Fix custom topology example; outdated import