code: def bind_port(requested_port):
    
    sockets = tornado.netutil.bind_sockets(requested_port)
  
    if requested_port != 0:
      return sockets, requested_port
  
    # Get the actual port number.
    for s in sockets:
      host, port = s.getsockname()[:2]
      if host == '0.0.0.0':
        return sockets, port
  
    raise RuntimeError('Could not determine the bound port.')
docs: Bind sockets to an available port, returning sockets and the bound port.