'Async version of delete_multi() -- note different return value.
Returns:
A UserRPC instance whose get_result() method returns None if
there was a network error, or a list of status values otherwise,
where each status corresponds to a key and is either
DELETE_SUCCESSFUL, DELETE_ITEM_MISSING, or DELETE_NETWORK_FAILURE
(see delete() docstring for details).'

def delete_multi_async(self, keys, seconds=0, key_prefix='', namespace=None, rpc=None):

    if (not isinstance(seconds, (int, long, float))):
        raise TypeError('Delete    timeout    must    be    a    number.')
    if (seconds < 0):
        raise ValueError('Delete    timeout    must    not    be    negative.')
    request = MemcacheDeleteRequest()
    self._add_app_id(request)
    _add_name_space(request, namespace)
    response = MemcacheDeleteResponse()
    for key in keys:
        delete_item = request.add_item()
        delete_item.set_key(_key_string(key, key_prefix=key_prefix))
        delete_item.set_delete_time(int(math.ceil(seconds)))
    return self._make_async_call(rpc, 'Delete', request, response, self.__delete_hook, None)
