On Jan 27, 6:57 pm, Jean-Paul Calderone <exar...@divmod.com> wrote: > On Tue, 27 Jan 2009 05:46:25 -0800 (PST), koranthala <koranth...@gmail.com> > wrote: > >Twisted, being twisted in its behavior is causing quite a lot of > >confusion in design decisions. > > I'm not sure I agree with your premise. ;) > > > > >I will put forward a comparison of reactor and non-reactor patterns. > >The code is not exact - whatever is shown is the gist of it. > > >For example, a message handler - in a usual scenario: > >class messageHandler: > > def run(): > > msg = self.get_next_msg() > > if not msg.send(): > > self.handle_failure() > > >To handle parallel execution, we will have to use threads, but the > >code flow is similar. > > >How do we do the same in a reactor pattern (Twisted)? > >msg.send will cause a deferred to be raised - the failure, if it > >happens will happen much later. > >i.e. other than sending messageHandler object in msg.send(), I cannot > >see any mechanism of running handle_failure. > > >In Twisted: > >class messageHandler: > > def run(): > > msg = self.get_next_msg() > > msg.send(self): > > >class msgClass: > > def send(o): > > d = deferred.addCallBack(success_handler, o).addErrBack > >(failure_handler, o) > > > def failure_handler(o): > > o.handle_failure() > > This doesn't look like a correct or faithful translation of the original. > Here are two possibilities. First: > > class messageHandler: > def run(): > msg = self.get_next_msg() > d = msg.send() > def cbSendFailed(result): > if not result: > self.handle_failure() > d.addErrback(cbSendFailed) > return d > > Next: > > class messageHandler: > @inlineCallbacks > def run(): > msg = self.get_next_msg() > if not (yield msg.send()): > self.handle_failure() > > These are both just straight translations from your version so as to > be able to handle a Deferred from `msg.send´. > > >Basically, what I find is that a lot of functional encapsulation is > >now lost by following reactor pattern. handle_failure is > >messageHandlers code and makes for pretty viewing if called from > >inside messageHandler itself. But, due to the twisted nature of > >reactor pattern, the msg Class - who is functionally a lower class to > >messageHandler invoking messageHandler's code. > > You don't need to lose anything. I don't know what your motivation was > for re-arranging the code when you wrote the Twisted version, but it doesn't > appear to have been necessary. > > >Is there a way to solve this in a more beautiful way? Am I missing > >something here? > > Hope this helps, > > Jean-Paul
Thank you Jean-Paul. My code is more complex than what I have mentioned. When I mentioned msg.send, the msg object actually gets the data from DB etc to send. And there are many other items being done. I will try to see whether I can change the code to incorporate what you mentioned. I rewrote most of my code after learning just raw deferreds - I had planned to study inlineCallbacks - but then it slipped my mind - now it has come to bit me. :-( -- http://mail.python.org/mailman/listinfo/python-list
