How to pass extra arguments to callback register functions with twisted python api?

Question

I have the following python code using the twisted API.

def function(self,filename):    
    def results(result):
       //do something
    for i in range(int(numbers)) :
        name = something that has to do with the value of i         
        df = function_which_returns_a defer(name)
        df.addCallback(results)

It uses the Twisted API. What i want to achieve is to pass to the callbacked function (results) the value of the name which is constructed in every iteration without changing the content of the functions_which_returns_a defer() function along with the deferred object of course. In every result of the functions_which_returns_a deffer the value of the name should be passed to results() to do something with this. I.e: at the first iteration when the execution reach the results function i need the function hold the result of the deffered object along with the value of name when i=0,then when i=1 the defered object will be passed with the value of name, and so on.So i need every time the result of the defer object when called with the name variable alond with the name variable. When i try to directly use the value of nameinside results() it holds always the value of the last iteration which is rationale, since function_which_returns_a defer(name) has not returned.

For the general case see callback - Python, how to pass an argument to a function pointer parameter? - Stack Overflow. In this specific case (twisted library) the solution below is better. — user202729
– user202729, Commented Aug 15, 2021 at 6:18

Jean-Paul Calderone · Accepted Answer · 2011-10-25 14:58:38Z

20

You can pass extra arguments to a Deferred callback at the Deferred.addCallback call site by simply passing those arguments to Deferred.addCallback:

def function(self,filename):    
    def results(result, name):
       # do something
    for i in range(int(numbers)) :
        name = something that has to do with the value of i         
        df = function_which_returns_a defer(name)
        df.addCallback(results, name)

You can also pass arguments by keyword:

        df.addCallback(results, name=name)

All arguments passed like this to addCallback (or addErrback) are passed on to the callback function.

answered Oct 25, 2011 at 14:58

Jean-Paul Calderone

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