Join a multicast group in python and receive data

joingroup.py

#!/usr/bin/env python3

import socket
import sys


def main(argv):
    multicast_group = argv[1]
    multicast_port = int(argv[2])
    interface_ip = argv[3]

    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
    sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 32)
    # See man socket(7)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)    
    
    sock.bind(('', multicast_port))
    sock.setsockopt(socket.SOL_IP, socket.IP_ADD_MEMBERSHIP,
                    socket.inet_aton(multicast_group) + socket.inet_aton(interface_ip))

    while True:
        received = sock.recv(1500)
        print('Received packet of {0} bytes'.format(len(received)))


if __name__ == '__main__':
    if len(sys.argv) != 4:
        print("Usage: {0} <group address> <port> <interface ip>".format(sys.argv[0]))
        sys.exit(1)
    main(sys.argv)

very neat! can I just ask, what is the interface ip and how does it differ from the multicast group argument? thanks!

The interface IP is the address of your local interface.
0.0.0.0 may work but this may be system dependent. Using 0.0.0.0 while having a route to 224.0.0.0/4 may work too.

oh cheers, brilliant!

Thanks for sharing, added following code

    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    # On macOS, this next option is particularly useful for multicast
    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)

before line 13: sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 32)
so that it won't run into error:
OSError: [Errno 48] Address already in use