<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def default_memcache_timeout_policy(key):
 """Default memcache timeout policy. This defers to _memcache_timeout on the Model class. Args: key: Key instance. Returns: Memcache timeout to use (integer), or None. """

    timeout = None
    if key is not None and isinstance(key, model.Key):
      modelclass = model.Model._kind_map.get(key.kind())
      if modelclass is not None:
        policy = getattr(modelclass, '_memcache_timeout', None)
        if policy is not None:
          if isinstance(policy, (int, long)):
            timeout = policy
          else:
            timeout = policy(key)
    return timeout