Python redis pubsub: что происходит с типами, когда они публикуются?

pub.py

import redis
import datetime
import time

def main():
    redis_host = '10.235.13.29'
        r = redis.client.StrictRedis(host=redis_host, port=6379)
        while True:
            now = datetime.datetime.now()
            print 'Sending {0}'.format(now)
            print 'data type is %s' % type(now)
            r.publish('clock', now)
            time.sleep(1)

if __name__ == '__main__':
  main()

ВЫХОД:

Sending 2014-10-08 13:10:58.338765
data type is <type 'datetime.datetime'>
Sending 2014-10-08 13:10:59.368707
data type is <type 'datetime.datetime'>
Sending 2014-10-08 13:11:00.378723
data type is <type 'datetime.datetime'>
Sending 2014-10-08 13:11:01.398132
data type is <type 'datetime.datetime'>
Sending 2014-10-08 13:11:02.419030
data type is <type 'datetime.datetime'>

sub.py

import redis
import threading
import time
import datetime

def callback():
    redis_host = '10.235.13.29'
    r = redis.client.StrictRedis(host=redis_host, port=6379)
    sub = r.pubsub()
    sub.subscribe('clock')
    while True:
        for m in sub.listen():
            #print m #'Recieved: {0}'.format(m['data'])
            now = datetime.datetime.now()
            print 'Recieved: %s at %s' % (m['data'], now)
            print 'Data type is %s' % type(m['data'])
            dur = 1
            print 'It took %s to receive' % dur

def main():
    t = threading.Thread(target=callback)
    t.setDaemon(True)
    t.start()
    while True:
        print 'Waiting'
        time.sleep(30)

if __name__ == '__main__':
    main()

ВЫХОД:

{}: ./sub.py
Waiting
Recieved: 1 at 2014-10-08 13:09:36.708088
Data type is <type 'long'>
It took 1 to receive
Recieved: 2014-10-08 13:09:37.629664 at 2014-10-08 13:09:37.630479
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:38.630661 at 2014-10-08 13:09:38.631585
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:39.632663 at 2014-10-08 13:09:39.633480
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:40.633662 at 2014-10-08 13:09:40.634464
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:41.634665 at 2014-10-08 13:09:41.635557
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:42.635662 at 2014-10-08 13:09:42.636673
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:43.642665 at 2014-10-08 13:09:43.643441
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:44.643663 at 2014-10-08 13:09:44.644582
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:45.644667 at 2014-10-08 13:09:45.673734
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:46.672918 at 2014-10-08 13:09:46.673874
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:47.673913 at 2014-10-08 13:09:47.675014
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:48.674920 at 2014-10-08 13:09:48.675804
Data type is <type 'str'>
It took 1 to receive
Recieved: 2014-10-08 13:09:49.675912 at 2014-10-08 13:09:49.677346
Data type is <type 'str'>

Тип изменен с datetime.datetime на str
Можно ли сохранить тип, потому что я пытаюсь найти продолжительность, которую я не могу вычесть из datetime obj в str?