'Recompute the domain to add new users and remove the one no longer matching the domain'

def _recompute_challenge_users(self):

    for challenge in self.filtered((lambda c: c.user_domain)):
        current_users = challenge.user_ids
        new_users = self._get_challenger_users(challenge.user_domain)
        if (current_users != new_users):
            challenge.user_ids = new_users
    return True
