code: def tracker_host_port_from_cli(rpc_tracker_str):
      """Extract hostname and (optional) port from strings
      like "1.2.3.4:9090" or "4.3.2.1".
  
      Used as a helper function to cover --rpc-tracker
      command line argument, in different subcommands.
  
      Parameters
      ----------
      rpc_tracker_str : str
          hostname (or IP address) and port of the RPC tracker,
          in the format 'hostname[:port]'.
  
      Returns
      -------
      rpc_hostname : str or None
          hostname or IP address, extracted from input.
      rpc_port : int or None
          port number extracted from input (9090 default).
      """
  
      rpc_hostname = rpc_port = None
  
      if rpc_tracker_str:
          parsed_url = urlparse("//%s" % rpc_tracker_str)
          rpc_hostname = parsed_url.hostname
          rpc_port = parsed_url.port or 9090
          logger.info("RPC tracker hostname: %s", rpc_hostname)
          logger.info("RPC tracker port: %s", rpc_port)
  
      return rpc_hostname, rpc_port
  
label_desc: Use image node_id 1 for calling a global function with example usage: tracker_host_port_from_cli(rpc_tracker_str) and returns: rpc_hostname,  rpc_port