human
Solve the following python programming problem given the following code:
@ classmethod 
@ gen.coroutine 
def _NotifyFollowers(cls, client, viewpoint_id, followers, invalidate, activity_func, inc_badge = False, always_notify = False) : 
    'Adds a notification for each of the given followers that the specified viewpoint has
    structurally changed. If "invalidate" is a dict, then uses that directly. Otherwise, assumes
    it\'s a function that takes a follower id and returns the invalidate dict for that follower.
    If "always_notify" is true, then always send notifications, even to removed followers.

    In order to minimize undesirable client artifacts caused by reads of half-committed data,
    we will commit updates in this order:

    1. In parallel:
       a. Create the activity.
       b. Update all Followed records (of all followers in the viewpoint).

    2. In parallel:
       a. Update update_seq in the viewpoint.
       b. Update viewed_seq in the sending follower.

    3. In parallel:
       a. For each follower:
          i. Create notification
          ii. Send alert
    ' 
    from viewfinder.backend.db.viewpoint import Viewpoint 
    from viewfinder.backend.op.alert_manager import AlertManager 
    operation = NotificationManager._GetOperation () 
    @ gen.coroutine 
    def _NotifyOneFollower(viewpoint, seq_num_pair, activity, follower, follower_settings) : 
        'Creates a notification for the follower and sends an alert if configured to do so.' 
        if (follower.IsRemoved () and (not always_notify)) : 
            return 
if ((invalidate is None) or isinstance (invalidate, dict)) : 
            foll_invalidate = invalidate 
else : 
            foll_invalidate = invalidate (follower.user_id) 
is_sending_user = (follower.user_id == operation.user_id) 
        notification = (yield Notification.CreateForUser (client, operation, follower.user_id, activity.name, invalidate = foll_invalidate, activity_id = activity.activity_id, viewpoint_id = viewpoint_id, seq_num_pair = seq_num_pair, inc_badge = (inc_badge and (not is_sending_user)))) 
        if (not...
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
all_follower_settings