UDPServer.py

#coding: utf-8
from socket import *
#using the socket module

#Define connection (socket) parameters
#Address + Port no
#Server would be running on the same host as Client
# change this port number if required
serverPort = 12000 

serverSocket = socket(AF_INET, SOCK_DGRAM)
#This line creates the server’s socket, called serverSocket. The first parameter indicates the address family; in particular,AF_INET indicates that the underlying network is using IPv4.The second parameter indicates that the socket is of type SOCK_DGRAM,which means it is a UDP socket (rather than a TCP socket, where we use SOCK_STREAM).

serverSocket.bind(('localhost', serverPort))
#The above line binds (that is, assigns) the port number 12000 to the server’s socket. In this manner, when anyone sends a packet to port 12000 at the IP address of the server (localhost in this case), that packet will be directed to this socket.
print 'The server is ready to receive'
while 1:
    message, clientAddress = serverSocket.recvfrom(2048)
    #receive data from the client, now we know who we are talking with
    
    modifiedMessage = message.upper()
    #change the case of the message received from client

    serverSocket.sendto(modifiedMessage, clientAddress)
    #send it back to client, need to specify the client address in sendto