client.py and server.py are a simple example of client/server
communication with sockets.  This could be run over the internet, but
the example below is run on a single machine (named 'thirty-two').

Note that ports 0 - 1023 are "well known", typically with only root access
see e.g. http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
   22  ssh
   53  dns
   80  http
  110  pop3
  443  https
ports 1024 - 49151, can be used by ordinary users
 8080  http common alternate
 1003  arbitrarily chosen for this example

-- server ------------- (start this first in terminal 1)

thirty-two:sockets$ python server.py 
server is listening at ('thirty-two', 10003) 

 connection 1 from ('192.168.1.33', 52131) 
 client sent 'message one sent at Sun Sep  9 17:26:08 2012' 
 client sent 'message two sent at Sun Sep  9 17:26:08 2012' 
 closing connection

 connection 2 from ('192.168.1.33', 52132) 
 client sent 'message one sent at Sun Sep  9 17:26:09 2012' 
 client sent 'message two sent at Sun Sep  9 17:26:09 2012' 
 closing connection

done - saw 2 connections
thirty-two:sockets$ 

-- client ------------- (run this in terminal 2 while server is running)

thirty-two:sockets$ python client.py 
opening connection to ('thirty-two', 10003)

sending : message one sent at Sun Sep  9 17:26:08 2012
server sent: client sent 'message one sent at Sun Sep  9 17:26:08 2012' 

sending : message two sent at Sun Sep  9 17:26:08 2012
server sent: client sent 'message two sent at Sun Sep  9 17:26:08 2012' 

closing connection

thirty-two:sockets$ python client.py 
opening connection to ('thirty-two', 10003)

sending : message one sent at Sun Sep  9 17:26:09 2012
server sent: client sent 'message one sent at Sun Sep  9 17:26:09 2012' 

sending : message two sent at Sun Sep  9 17:26:09 2012
server sent: client sent 'message two sent at Sun Sep  9 17:26:09 2012' 

closing connection
thirty-two:sockets$