Returning values from callback(s) in Python

Question

I am currently looking at trying to use a callback in Python.

What I would like to do is return a value from the callback and then use this return value for conditional processing. So for example if the user enters "Y" I would like to print something to the console.

As I am new to Python the code below is as close as I can get currently but:

a) I am not sure if it is the Pythonic way of doing it

b) the correct way of doing it?

    class Observable:
        def subscribe(self,callback):
            self.callback = callback

        def fire(self):
            self.callback()

    class CallBackStuff:
        def doCallback(self):
            userInput = raw_input("Please enter Y or N?")
            return userInput

    if __name__ == '__main__':
        s = CallBackStuff()
        o = Observable()
        o.subscribe(s.doCallback)
        t = o.fire()
        print t

why not just return self.callback() ?

BartoszKP
– BartoszKP

2013-10-25 09:24:59 +00:00
Commented Oct 25, 2013 at 9:24 — BartoszKP
– BartoszKP, Commented Oct 25, 2013 at 9:24
@GamesBrainiac Related but no return value there I think

BartoszKP
– BartoszKP

2013-10-25 09:25:52 +00:00
Commented Oct 25, 2013 at 9:25 — BartoszKP
– BartoszKP, Commented Oct 25, 2013 at 9:25
@BartoszKP You're right.

Nafiul Islam
– Nafiul Islam

2013-10-25 09:26:40 +00:00
Commented Oct 25, 2013 at 9:26 — Nafiul Islam
– Nafiul Islam, Commented Oct 25, 2013 at 9:26

Andy Rimmer · Accepted Answer · 2013-10-25 10:04:02Z

6

The easiest way I can think of to do this in your code is to just store the input as a variable in the CallBackStuff object. Then after you've called the call-back function, you can just access the input data from the CallBackStuff instance. Example below.

class Observable:
    def subscribe(self,callback):
        self.callback = callback

    def fire(self):
        self.callback()

class CallBackStuff:
    storedInput = None # Class member to store the input
    def doCallback(self):
        self.storedInput = raw_input("Please enter Y or N?")

if __name__ == '__main__':
    s = CallBackStuff()
    o = Observable()
    o.subscribe(s.doCallback)
    o.fire()
    print s.storedInput # Print stored input from call-back object

answered Oct 25, 2013 at 10:04

Andy Rimmer

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Siva Cn · Accepted Answer · 2013-10-25 09:56:52Z

1

class Observable(object):
    def __call__(self, fun):
        return fun()


class Callback(object):
    def docallback(self):
        inp = raw_input()
        return inp

if __name__ == "__main__":
    print Observable()(Callback().docallback)

answered Oct 25, 2013 at 9:56

Siva Cn

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