[Twisted-Python] Calling deferred within a callback, good or bad idea ?
Hi, I have to call a web service then process the answer, according to the answer I may have to call the service again. The traditional way to go would be : condition = 1 while condition: message = callWebService() condition = processMessage(message) Here is what I do : def function(): def myCalback(message): condition = processMessage(message) if condition: deferred = callWebService() deferred.addCallback(myCallback) deferred = callWebService() deferred.addCallback(myCallback) I was wondering if it was the way to go or if there was a better way, since I'm not quite sure about the impact of calling new deffered within a callback. Thanks, Stéphane
Selon Stéphane Brault <stephane_brault@yahoo.fr>:
Hi, I have to call a web service then process the answer, according to the answer I may have to call the service again. The traditional way to go would be : condition = 1 while condition: message = callWebService() condition = processMessage(message)
Here is what I do : def function():
def myCalback(message): condition = processMessage(message) if condition: deferred = callWebService() deferred.addCallback(myCallback)
deferred = callWebService() deferred.addCallback(myCallback)
I was wondering if it was the way to go or if there was a better way, since I'm not quite sure about the impact of calling new deffered within a callback.
You may have a recursion problem with this kind of code (I'm not quite sure when it happens but it does). One good way is to use deferredGenerator: # Not tested def function(): condition = True while condition: wfd = defer.waitForDeferred(callWebService()) yield wfd condition = wfd.getResult() function = defer.deferredGenerator(function) -- Thomas
Thanks Thomas, I'll try your solution. Stéphane ----- Message d'origine ---- De : Thomas Hervé <therve@free.fr> À : Twisted general discussion <twisted-python@twistedmatrix.com> Envoyé le : Vendredi, 19 Mai 2006, 8h26mn 03s Objet : Re: [Twisted-Python] Calling deferred within a callback, good or bad idea ? Selon Stéphane Brault <stephane_brault@yahoo.fr>:
Hi, I have to call a web service then process the answer, according to the answer I may have to call the service again. The traditional way to go would be : condition = 1 while condition: message = callWebService() condition = processMessage(message)
Here is what I do : def function():
def myCalback(message): condition = processMessage(message) if condition: deferred = callWebService() deferred.addCallback(myCallback)
deferred = callWebService() deferred.addCallback(myCallback)
I was wondering if it was the way to go or if there was a better way, since I'm not quite sure about the impact of calling new deffered within a callback.
You may have a recursion problem with this kind of code (I'm not quite sure when it happens but it does). One good way is to use deferredGenerator: # Not tested def function(): condition = True while condition: wfd = defer.waitForDeferred(callWebService()) yield wfd condition = wfd.getResult() function = defer.deferredGenerator(function) -- Thomas _______________________________________________ Twisted-Python mailing list Twisted-Python@twistedmatrix.com http://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
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Stéphane Brault -
Thomas Hervé