title: pythons socket.sendto third argument
body: <p>I'm using python socket module, and I read that you can use either 2 or 3 arguments when using <code>socket.sendto()</code> command. you can specify address and message, but you can also send flags.
  I was wondering what these flags are? I couldn't find any information about it. what happens when you send them? what is the default value? (when you don't specify a flag) what do they do?</p>