docs: def address(addr):
      """
      A special argument type that splits a string on ':' and transforms
      the result into a tuple of host and (integer) port.
      """
  
      if ':' in addr:
          # Using rpartition here means we should be able to support
          # IPv6, but only with a strict syntax
          host, _sep, port = addr.rpartition(':')
  
          # Convert the port to a number
          try:
              port = int(port)
          except ValueError:
              raise ValueError("invalid port number %r" % port)
  
          addr = (host, port)
  
      return addr