title: Notification of key expiration in redis python
body: <p>I would like to be notified when a volatile key expires in my redis store. The redis website provides some description of how this might be achieved in <a href="http://redis.io/topics/notifications">http://redis.io/topics/notifications</a>, but I am wondering if it can be done using the python redis api. </p>
  
  <p>After setting:<code>notify-keyspace-events Ex</code> in my redis.conf file</p>
  
  <p>and running this as a test:</p>
  
  <pre><code>import redis
  import config
  
  client = redis.StrictRedis.from_url(config.REDIS_URI) 
  client.set_response_callback('EXPIRE',callback)
  client.set('a', 1)
  client.expire('a',5)
  </code></pre>
  
  <p><code>callback()</code> only gets called when <code>client.expire('a',5)</code> gets called, but not five seconds later as expected </p>