code: def purge(self, key, ttl):
          
          mors_to_purge = []
          now = time.time()
          with self._mor_lock:
              # Don't change the dict during iteration!
              # First collect the names of the Mors to remove...
              for name, mor in iteritems(self._mor[key]):
                  age = now - mor['creation_time']
                  if age > ttl:
                      mors_to_purge.append(name)
  
              # ...then actually remove the Mors from the cache.
              for name in mors_to_purge:
                  del self._mor[key][name]
docs: Remove all the items in the cache for the given key that are older than
          ttl seconds.
          If the key is not in the cache, raises a KeyError.