def METHOD_NAME(
    start: Optional[datetime] = None, end: Optional[datetime] = None
):
    if start is None or end is None:
        start, end = get_yesterday_datetime_range()
    yesterdays_comments = list(get_comment_updates(start, end))
    def key_func(n):
        return (n.object.user_id, n.object.id, n.timestamp)
    yesterdays_comments = sorted(yesterdays_comments, key=key_func)
    for user_id, group in groupby(yesterdays_comments, lambda n: n.object.user_id):
        if user_id is None:
            continue
        notifications = list(group)
        user = notifications[0].object.user
        send_update(notifications, user=user)