Re : [Twisted-Python] Calling deferred within a callback, good or bad idea ?

May 21, 2006


      Thanks Thomas,
 I'll try your solution.
 
 Stéphane

----- Message d'origine ----
De : Thomas Hervé <therve@free.fr>
Ã€ : Twisted general discussion <twisted-python@twistedmatrix.com>
EnvoyÃ© le : Vendredi, 19 Mai 2006, 8h26mn 03s
ObjetÂ : Re: [Twisted-Python] Calling deferred within a callback, good or bad idea ?

Selon StÃ©phane 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

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Re : [Twisted-Python] Calling deferred within a callback, good or bad idea ?

Stéphane Brault