Added an example of how to make an empty Mininet and add things to it.

examples/emptynet.py

+#!/usr/bin/python
+
+"""
+This example shows how to create an empty Mininet() object 
+(without a topology object) and add nodes to it manually.
+"""
+
+from mininet.net import Mininet
+from mininet.node import Controller
+from mininet.cli import CLI
+from mininet.log import setLogLevel
+
+def emptyNet():
+
+    "Create an empty network and add nodes to it."
+    
+    net = Mininet( controller=Controller )
+
+    print "*** Adding controller"
+    c0 = net.addController( 'c0' )
+    
+    print "*** Adding hosts"
+    h1 = net.addHost( 'h1', ip='10.0.0.1' )
+    h2 = net.addHost( 'h2', ip='10.0.0.2' )
+    
+    print "*** Adding switch"
+    s3 = net.addSwitch( 's3' )
+    
+    print "*** Creating links"
+    h1.linkTo( s3 )
+    h2.linkTo( s3 )
+    
+    print "*** Starting network"
+    net.build()
+    net.start()
+    
+    print "*** Running CLI"
+    setLogLevel( 'info' )
+    CLI( net )
+    
+    print "*** Stopping network"
+    net.stop()
+    
+if __name__ == '__main__':
+    emptyNet()