Now that the steps are clear, let's create a simple echo server. First the imports:

from socket import *

Then the constants that defines the host, port, buffer size and the address tuple to be used with bind().

from socket import *
HOST = 'localhost'
PORT = 21567
BUFSIZ = 1024
ADDR = (HOST, PORT)

Then we create the server side socket and bind it to the host and the port. Then comes the max queue size to 2:

from socket import *
HOST = 'localhost'
PORT = 21567
BUFSIZ = 1024
ADDR = (HOST, PORT)
serversock = socket(AF_INET, SOCK_STREAM)
serversock.bind(ADDR)
serversock.listen(2)

Now, to make it listen for incoming requests continuously, place the accept() method in a while loop. This is not the most preferred mode. The preferred way will be discussed in the next section:

from socket import *
HOST = 'localhost'
PORT = 21567
BUFSIZ = 1024
ADDR = (HOST, PORT)
serversock = socket(AF_INET, SOCK_STREAM)
serversock.bind(ADDR)
serversock.listen(2)

while 1:
       print 'waiting for connection…'
       clientsock, addr = serversock.accept()
       print '…connected from:', addr
       :
       :

Next, receive the data from the client and echo it back. This has to continue until the client doesn’t send the null data or ctrl+c. To achieve this, use a while loop again and then close the connection when done.

from socket import *
HOST = 'localhost'
PORT = 21567
BUFSIZ = 1024
ADDR = (HOST, PORT)
serversock = socket(AF_INET, SOCK_STREAM)
serversock.bind(ADDR)
serversock.listen(2)

while 1:
       print 'waiting for connection…'
       clientsock, addr = serversock.accept()
       print '…connected from:', addr

       while 1:
             data = clientsock.recv(BUFSIZ)
             if not data: break
                   clientsock.send(‘echoed’, data)
  
       clientsock.close()

serversock.close()

That’s all for the server. Now for the client. The only exception is that there is no bind(), accept() and listen().

from socket import *

HOST = 'localhost'
PORT = 21567
BUFSIZ = 1024
ADDR = (HOST, PORT)

tcpCliSock = socket(AF_INET, SOCK_STREAM)
tcpCliSock.connect(ADDR)

       while 1:
             data = raw_input('> ')
             if not data: break 
             tcpCliSock.send(data)
            data = tcpCliSock.recv(1024)
             if not data: break 
       print data

tcpCliSock.close()