Hi, I 'd like to add a pre-processing and post-processing callback in a deferred callback list. I did somthing like this : my_defer = getADeferredForSomething() new_defer = defer.Deferred() new_defer.addCallback(preprocessing) new_defer.chainDeferred(my_defer) new_defer.addCallback(postprocessing) my_defer = new_defer My problem is that postprocessing doesn't receive the result of the last callback in my_defer, but it reveive None. This can be explained in twisted source by that chainDeferred(d) is equivalent to addCallbacks(d.callback, d.errback), but this two methods are not really sort of callback methods for deferred coz they didn't return a result. So I patched Deferred class to add "return self.result", and it works well : Deferred_old = defer.Deferred class Deferred_new(Deferred_old): def callback(self, result): Deferred_old.callback(self, result) return self.result def errback(self, fail=None): Deferred_old.errback(self, fail) return self.result defer.Deferred = Deferred_new Notes by doing this you can also get final result when firing the callbacks : final_result = my_defer.callback(result) I dunno if this patch will fail something else in twisted. fc.