title: listening for multicast traffic on mutiple networks
body: <p>I currently have the following code that receive multicast data.</p>
  
  <pre><code>sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
  sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
  sock.bind(('', 24003))
  mreq = struct.pack("=4sl", socket.inet_aton("238.210.10.1"), socket.INADDR_ANY)
  sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
  </code></pre>
  
  <p>I have two network cards but the code only listens to messages sent to 127.0.0.1. How do I listen to all multicast message on any network card? without hard-coding them.</p>