docs: def pytwis_command_processor(twis, auth_secret, args):
      """Process the parsed command.
  
      Parameters
      ----------
      twis: Pytwis
          A Pytwis instance which interacts with the Redis database of the Twitter toy clone.
      auth_secret: str
          The authentication secret of a logged-in user.
      args:
          The parsed command output by pytwis_command_parser().
      """
      command = args[pytwis_clt_constants.ARG_COMMAND]
  
      if command == pytwis_clt_constants.CMD_REGISTER:
          succeeded, result = twis.register(args[pytwis_clt_constants.ARG_USERNAME],
                                            args[pytwis_clt_constants.ARG_PASSWORD])
          if succeeded:
              print('Registered {}'.format(args[pytwis_clt_constants.ARG_USERNAME]))
          else:
              print("Couldn't register {} with error = {}".\
                    format(args[pytwis_clt_constants.ARG_USERNAME],
                           result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_LOGIN:
          succeeded, result = twis.login(args[pytwis_clt_constants.ARG_USERNAME],
                                         args[pytwis_clt_constants.ARG_PASSWORD])
          if succeeded:
              auth_secret[0] = result[pytwis_constants.AUTH_KEY]
              print('Logged into username {}'.format(args[pytwis_clt_constants.ARG_USERNAME]))
          else:
              print("Couldn't log into username {} with error = {}".\
                    format(args[pytwis_clt_constants.ARG_USERNAME],
                           result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_LOGOUT:
          succeeded, result = twis.logout(auth_secret[0])
          if succeeded:
              auth_secret[0] = result[pytwis_constants.AUTH_KEY]
              print('Logged out of username {}'.format(result[pytwis_constants.USERNAME_KEY]))
          else:
              print("Couldn't log out with error = {}".format(result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_CHANGE_PASSWORD:
          succeeded, result = twis.change_password(auth_secret[0],
                                                   args[pytwis_clt_constants.ARG_OLD_PASSWORD],
                                                   args[pytwis_clt_constants.ARG_NEW_PASSWORD])
          if succeeded:
              auth_secret[0] = result[pytwis_constants.AUTH_KEY]
              print('Changed the password')
          else:
              print("Couldn't change the password with error = {}".\
                    format(result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_GET_USER_PROFILE:
          succeeded, result = twis.get_user_profile(auth_secret[0])
          if succeeded:
              print('Got the user profile')
              print('=' * 20)
              for key, value in result.items():
                  print('{}: {}'.format(key, value))
              print('=' * 20)
          else:
              print("Couldn't get the user profile with error = {}".\
                    format(result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_POST:
          succeeded, result = twis.post_tweet(auth_secret[0], args['tweet'])
          if succeeded:
              print('Posted the tweet')
          else:
              print("Couldn't post the tweet with error = {}".\
                    format(result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_FOLLOW:
          succeeded, result = twis.follow(auth_secret[0],
                                          args[pytwis_clt_constants.ARG_FOLLOWEE])
          if succeeded:
              print('Followed username {}'.format(args[pytwis_clt_constants.ARG_FOLLOWEE]))
          else:
              print("Couldn't follow the username {} with error = {}".\
                    format(args[pytwis_clt_constants.ARG_FOLLOWEE],
                           result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_UNFOLLOW:
          succeeded, result = twis.unfollow(auth_secret[0],
                                            args[pytwis_clt_constants.ARG_FOLLOWEE])
          if succeeded:
              print('Unfollowed username {}'.format(args[pytwis_clt_constants.ARG_FOLLOWEE]))
          else:
              print("Couldn't unfollow the username {} with error = {}".\
                    format(args[pytwis_clt_constants.ARG_FOLLOWEE],
                           result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_GET_FOLLOWERS:
          succeeded, result = twis.get_followers(auth_secret[0])
          if succeeded:
              print('Got the list of {} followers'.\
                    format(len(result[pytwis_constants.FOLLOWER_LIST_KEY])))
              print('=' * 20)
              for follower in result[pytwis_constants.FOLLOWER_LIST_KEY]:
                  print('\t' + follower)
              print('=' * 20)
          else:
              print("Couldn't get the follower list with error = {}".\
                    format(result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_GET_FOLLOWINGS:
          succeeded, result = twis.get_following(auth_secret[0])
          if succeeded:
              print('Got the list of {} followings'.\
                    format(len(result[pytwis_constants.FOLLOWING_LIST_KEY])))
              print('=' * 60)
              for following in result[pytwis_constants.FOLLOWING_LIST_KEY]:
                  print('\t' + following)
              print('=' * 60)
          else:
              print("Couldn't get the following list with error = {}".\
                    format(result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_TIMELINE:
          succeeded, result = twis.get_timeline(auth_secret[0],
                                                args[pytwis_clt_constants.ARG_MAX_TWEETS])
          if succeeded:
              if auth_secret[0] != '':
                  print('Got {} tweets in the user timeline'.\
                        format(len(result[pytwis_constants.TWEETS_KEY])))
              else:
                  print('Got {} tweets in the general timeline'.\
                        format(len(result[pytwis_constants.TWEETS_KEY])))
              print_tweets(result[pytwis_constants.TWEETS_KEY])
          else:
              if auth_secret[0] != '':
                  print("Couldn't get the user timeline with error = {}".\
                        format(result[pytwis_constants.ERROR_KEY]))
              else:
                  print("Couldn't get the general timeline with error = {}".\
                        format(result[pytwis_constants.ERROR_KEY]))
      elif command == pytwis_clt_constants.CMD_GET_USER_TWEETS:
          # Get the username of the currently logged-in user if no username is given.
          if args[pytwis_clt_constants.ARG_USERNAME] is None:
              succeeded, result = twis.get_user_profile(auth_secret[0])
              if succeeded:
                  args[pytwis_clt_constants.ARG_USERNAME] = result[pytwis_constants.USERNAME_KEY]
                  print('No username is given, so use the currently logged-in user {}'.\
                        format(args[pytwis_clt_constants.ARG_USERNAME]))
              else:
                  print("Couldn't get the username of the currently logged-in user with error = {}".\
                        format(result[pytwis_constants.ERROR_KEY]))
                  return
  
          succeeded, result = twis.get_user_tweets(auth_secret[0],
                                                   args[pytwis_clt_constants.ARG_USERNAME],
                                                   args[pytwis_clt_constants.ARG_MAX_TWEETS])
          if succeeded:
              print('Got {} tweets posted by {}'.format(len(result[pytwis_constants.TWEETS_KEY]),
                                                        args[pytwis_clt_constants.ARG_USERNAME]))
              print_tweets(result[pytwis_constants.TWEETS_KEY])
          else:
              print("Couldn't get the tweets posted by {} with error = {}".\
                    format(args[pytwis_clt_constants.ARG_USERNAME],
                           result[pytwis_constants.ERROR_KEY]))
      else:
          pass