docs: def commandstr(command):
      """Convert command into string."""
      if command == CMD_MESSAGE_ERROR:
          msg = "CMD_MESSAGE_ERROR"
      elif command == CMD_MESSAGE_LIST:
          msg = "CMD_MESSAGE_LIST"
      elif command == CMD_MESSAGE_PASSWORD:
          msg = "CMD_MESSAGE_PASSWORD"
      elif command == CMD_MESSAGE_MP3:
          msg = "CMD_MESSAGE_MP3"
      elif command == CMD_MESSAGE_DELETE:
          msg = "CMD_MESSAGE_DELETE"
      elif command == CMD_MESSAGE_VERSION:
          msg = "CMD_MESSAGE_VERSION"
      elif command == CMD_MESSAGE_CDR_AVAILABLE:
          msg = "CMD_MESSAGE_CDR_AVAILABLE"
      elif command == CMD_MESSAGE_CDR:
          msg = "CMD_MESSAGE_CDR"
      else:
          msg = "CMD_MESSAGE_UNKNOWN"
      return msg