human
Solve the following python programming problem given the following code:
def _enqueue_request(self, request, spider) : 
    (key, slot) = self._get_slot (request, spider) 
    request.meta ['download_slot'] = key 
    def _deactivate(response) : 
        slot.active.remove (request) 
        return response 
slot.active.add (request) 
    deferred = defer.Deferred ().addBoth (_deactivate) 
    slot.queue.append ((request, slot)) 
    self._process_queue (spider, slot) 
    return deferred 

    
    

    Fix the buggy line: slot.queue.append ((request, slot))
assistant
#Here is Python program to fix the buggy line: slot.

slot.queue.append ((request, deferred))