Use print function

examples/nat.py

@@ -4,18 +4,21 @@
 Example to create a Mininet topology and connect it to the internet via NAT
 """
 
+from __future__ import print_function
+
 from mininet.cli import CLI
 from mininet.log import lg
 from mininet.topolib import TreeNet
 
+
 if __name__ == '__main__':
     lg.setLogLevel( 'info')
     net = TreeNet( depth=1, fanout=4 )
     # Add NAT connectivity
     net.addNAT().configDefault()
     net.start()
-    print "*** Hosts are running and should have internet connectivity"
-    print "*** Type 'exit' or control-D to shut down network"
+    print( "*** Hosts are running and should have internet connectivity" )
+    print( "*** Type 'exit' or control-D to shut down network" )
     CLI( net )
     # Shut down NAT
     net.stop()