A unique Python redis-based queue with delay

import time
import redis


REDIS_ADDRESS = '127.0.0.1'


class UniqueMessageQueueWithDelay(object):
    """A message queue based on the Redis sorted set data type. Duplicate items
    in the queue are not allowed. When a duplicate item is added to the queue,
    the new item is added, and the old duplicate item is removed. A delay may be
    specified when adding items to the queue. Items will only be popped after
    the delay has passed. Pop() is non-blocking, so polling must be used. The
    name of the queue == the Redis key for the sorted set.
    """
    def __init__(self, name):
        self.name = name
        self.redis = redis.Redis(REDIS_ADDRESS)

    def add(self, data, delay=0):
        """Add an item to the queue. delay is in seconds.
        """
        score = time.time() + delay
        self.redis.zadd(self.name, data, score)
        debug('Added %.1f, %s' % (score, data))

    def pop(self):
        """Pop one item from the front of the queue. Items are popped only if
        the delay specified in the add() has passed. Return False if no items
        are available.
        """
        min_score = 0
        max_score = time.time()
        result = self.redis.zrangebyscore(
            self.name, min_score, max_score, start=0, num=1, withscores=False)
        if result == None:
            return False
        if len(result) == 1:
            debug('Popped %s' % result[0])
            return result[0]
        else:
            return False

    def remove(self, data):
        return self.redis.zrem(self.name, data)


def debug(msg):
    print msg


def test_queue():
    u = UniqueMessageQueueWithDelay('myqueue')

    # add items to the queue
    for i in [0, 1, 2, 3, 4, 0, 1]:
        data = 'Item %d' % i
        delay = 5
        u.add(data, delay)
        time.sleep(0.1)

    # get items from the queue
    while True:
        print
        result = u.pop()
        print result
        if result != False:
            u.remove(result)
        time.sleep(1)


if __name__ == '__main__':
    test_queue()