'Add Task to subscription filter'

def add_task_subscription(self, task_id):

    subscription = self.subscription
    rfilter = self.rfilter
    if subscription['get_vars'].get(rfilter, None):
        ids = subscription['get_vars'][rfilter]
        ids += (',' + task_id)
    else:
        ids = task_id
    sfilter = [[rfilter, ids], self.exclude]
    subscription['filters'] = json.dumps(sfilter)
    return self.update_subscription()
