This script automatically adds all followers of a twitter user to an existing list. It checks every hour for new followers.

autofollowertolist.py

from time import gmtime, strftime, sleep
from twython import Twython

app_key = 'xxx'
app_secret = 'xxx'
access_token = 'xxx'
access_token_secret = 'xxx'

list_id = u'xxxxxxx'
screen_name = u'xxxxx'

t = Twython(app_key=app_key, 
            app_secret=app_secret, 
            callback_url='http://google.com/', 
            oauth_token=access_token,
            oauth_token_secret=access_token_secret)

while True:   

    followers = t.getFollowersIDs(screen_name=screen_name)[u'ids']
    follower_names = [t.lookupUser(user_id=id)[0][u'screen_name'] for id in followers]

    raw_members = t.getListMembers(list_id=list_id)[u'users']
    n_raw_members = len(raw_members)

    members = [raw_members[i][u'id'] for i in range(n_raw_members)]

    for i, follower in enumerate(followers):
        try:
           _ = members.index(follower)
        except ValueError:
            timestamp = strftime("%a, %d %b %Y %H:%M:%S", gmtime())
            result = t.addListMember(list_id=list_id, user_id=unicode(follower))
            new_n_members = result[u'member_count']
            log = ' added ' + str(follower_names[i]) + ' to list (' + str(new_n_members) + ')'
            output = timestamp + log
            print 
    sleep(3600)