docs: def fetch_twitter_lists_for_user_ids_generator(twitter_app_key,
                                                 twitter_app_secret,
                                                 user_id_list):
      """
      Collects at most 500 Twitter lists for each user from an input list of Twitter user ids.
  
      Inputs: - twitter_app_key: What is says on the tin.
              - twitter_app_secret: Ditto.
              - user_id_list: A python list of Twitter user ids.
  
      Yields: - user_twitter_id: A Twitter user id.
              - twitter_lists_list: A python list containing Twitter lists in dictionary (json) format.
      """
      ####################################################################################################################
      # Log into my application.
      ####################################################################################################################
      twitter = login(twitter_app_key,
                      twitter_app_secret)
  
      ####################################################################################################################
      # For each user, gather at most 500 Twitter lists.
      ####################################################################################################################
      get_list_memberships_counter = 0
      get_list_memberships_time_window_start = time.perf_counter()
      for user_twitter_id in user_id_list:
          # Make safe twitter request.
          try:
              twitter_lists_list, get_list_memberships_counter, get_list_memberships_time_window_start\
                  = safe_twitter_request_handler(twitter_api_func=twitter.get_list_memberships,
                                                 call_rate_limit=15,
                                                 call_counter=get_list_memberships_counter,
                                                 time_window_start=get_list_memberships_time_window_start,
                                                 max_retries=5,
                                                 wait_period=2,
                                                 user_id=user_twitter_id,
                                                 count=500,
                                                 cursor=-1)
              # If the call is succesful, yield the list of Twitter lists.
              yield user_twitter_id, twitter_lists_list
          except twython.TwythonError:
              # If the call is unsuccesful, we do not have any Twitter lists to store.
              yield user_twitter_id, None
          except URLError:
              # If the call is unsuccesful, we do not have any Twitter lists to store.
              yield user_twitter_id, None
          except BadStatusLine:
              # If the call is unsuccesful, we do not have any Twitter lists to store.
              yield user_twitter_id, None