#!/usr/bin/env python
     # encoding: utf-8
     #
     # Copyright (c) 2010 Doug Hellmann.  All rights reserved.
     #
     """Sending multicast messages.
     """
     #end_pymotw_header
     
     import socket
     import struct
     import sys
     
     message = 'very important data'
     multicast_group = ('224.3.29.71', 10000)
     
     # Create the datagram socket
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     
     # Set a timeout so the socket does not block indefinitely when trying
     # to receive data.
     sock.settimeout(0.2)
     
     # Set the time-to-live for messages to 1 so they do not go past the
     # local network segment.
     ttl = struct.pack('b', 1)
     sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl)
     
     try:
     
         # Send data to the multicast group
         print >>sys.stderr, 'sending "%s"' % message
         sent = sock.sendto(message, multicast_group)
     
         # Look for responses from all recipients
         while True:
             print >>sys.stderr, 'waiting to receive'
             try:
                 data, server = sock.recvfrom(16)
             except socket.timeout:
                 print >>sys.stderr, 'timed out, no more responses'
                 break
             else:
                 print >>sys.stderr, 'received "%s" from %s' % (data, server)
     
     finally:
         print >>sys.stderr, 'closing socket'
         sock.close()