Dear List: I am having a heck of a time trying to figure out why this traceback is happening, and I was hoping that you could shed some light on the situation. I am sorry for bothering you with this simple thing, but I can't seem to figure it out! The code and traceback are below. The traceback only happens when I call httprequest.writeResponse(httpresponse) from a callback. When the same code is called inline and not in a deferred, it works just fine. Even stranger is that the response is written to the client even though the traceback occurs. An explanation of what I am trying to do: A consumer requests data. If there is data in the queue when the consumer first checks, return the result right away. If there is no data present, return a deferred and wait. When the producer inserts data into the queue, check if there is a consumer waiting. If so, begin callback chain on consumer. The code works fine (no traceback) in the case where there is no deferred needed (in QueueCache.maybedefer). When there is a deferred, the traceback happens during the callback (in QueueCache.put). Again, the consumer actually gets the correct result, but the traceback still occurs! Any ideas? Thanks in advance! ~P from twisted.internet import reactor, defer from twisted.web2 import http, responsecode import Queue TIMEOUT = 10 def respond(result, httprequest): httpresponse = http.Response(responsecode.OK, {}, stream=result) httprequest.writeResponse(httpresponse) class QueueCache(object): def __init__(self): self.queue = {} self.defer = {} def get_data(self, xSig): return self.get_queue(xSig).get_nowait() def push_data(self, xSig, value): self.get_queue(xSig).put(value) def get_queue(self, xSig): try: return self.queue[xSig] except KeyError: q = Queue.Queue() self.queue[xSig] = q return q def defer_request(self, xSig, httprequest): if self.defer.has_key(xSig): raise Exception("Client %s already has a deferred request!" %(xSig)) def timeout(deferred, request): xSig = request.args['X-Signature'][0] try: self.defer.pop(xSig) except KeyError: print 'Timeout called and xSig `%s` was not in cache!' % xSig respond('ACK',request) d = defer.Deferred() d.addCallback(respond, httprequest) d.setTimeout(TIMEOUT, timeout, httprequest) self.defer[xSig] = d return d def put(self, data): xSig = data['X-Signature'] try: d = self.defer.pop(xSig) d.callback(data['message']) except KeyError: self.push_data(xSig,data) def maybedefer(self, httprequest): xSig = httprequest.args['X-Signature'][0] try: data = self.get_data(xSig) result = http.Response( responsecode.OK, {}, stream=data['message'] ) except Queue.Empty: result = self.defer_request(xSig, httprequest) return result ----------------------------------------------------------------------------------------------------- 2007-09-25 18:38:38-0700 [-] Original exception: 2007-09-25 18:38:38-0700 [-] Unhandled Error Traceback (most recent call last): File "C:\Projects\PyServer\twisted\internet\defer.py", line 304, in _startRunCallbacks File "C:\Projects\PyServer\twisted\internet\defer.py", line 317, in _runCallbacks File "C:\Projects\PyServer\twisted\internet\defer.py", line 281, in _continue File "C:\Projects\PyServer\twisted\internet\defer.py", line 277, in unpause --- <exception caught here> --- File "C:\Projects\PyServer\twisted\internet\defer.py", line 317, in _runCallbacks File "C:\Projects\PyServer\twisted\web2\server.py", line 518, in _cbFinishRender exceptions.TypeError: html is not a resource or a response 2007-09-25 18:38:39-0700 [-] Unhandled error in Deferred: 2007-09-25 18:38:39-0700 [-] Unhandled Error Traceback (most recent call last): File "C:\Projects\PyServer\twisted\internet\defer.py", line 317, in _runCallbacks File "C:\Projects\PyServer\twisted\web2\server.py", line 476, in _processingFailed File "C:\Projects\PyServer\twisted\internet\defer.py", line 200, in addErrback File "C:\Projects\PyServer\twisted\internet\defer.py", line 182, in addCallbacks --- <exception caught here> --- File "C:\Projects\PyServer\twisted\internet\defer.py", line 317, in _runCallbacks File "C:\Projects\PyServer\twisted\web2\server.py", line 492, in _processingReallyFailed File "C:\Python24\lib\site-packages\twisted\web2\http.py", line 446, in writeResponse self.chanRequest.writeHeaders(response.code, response.headers) File "C:\Projects\PyServer\twisted\web2\channel\http.py", line 431, in writeHeaders File "C:\Projects\PyServer\twisted\web2\channel\http.py", line 466, in _writeHeaders exceptions.AttributeError: 'HTTPChannelRequest' object has no attribute 'transport'