new_contents: from mininet.topo import Topo
  
  class DiamondTopo(Topo):
      def __init__( self ):
          Topo.__init__( self )
          h1 = self.addHost('h1')
          h2 = self.addHost('h2')
          s1 = self.addSwitch('s1')
          s2 = self.addSwitch('s2')
          s3 = self.addSwitch('s3')
          s4 = self.addSwitch('s4')
          self.addLink(s1,h1)
          self.addLink(s4,h2)
          self.addLink(s1,s2)
          self.addLink(s1,s3)
          self.addLink(s2,s4)
          self.addLink(s3,s4)
  
  topos = { 'diamond': ( lambda: DiamondTopo() ) }
  
subject: Add diamond topology