CODEWITHSUNDEEP
pythonpython-3.xcallbacklistener
Riskhan
Riskhan

Reputation: 4470

Implementation of callback or listener in python

I just entered into python programming (i have experience with java). I want to implement callback/listener in a class. I confused with available samples. I just implemented a sample. Please guide me

my python class as follows

class myClass:
    def __init__(self):
        self.__result = 0

    def connect(self):
        self.__result = 1

my main python code as follows

import myClass

def on_connect(result):
    print("Connected with result code "+result)

myclass = myClass()
myclass.on_connect = on_connect

myclass.connect()

I just wanted to receive result in on_connect method main code. How to modify the myClass for this ?

Thanks in advance

Upvotes: 1

Views: 9357

Answers (2)

Fabio Caccamo
Fabio Caccamo

Reputation: 1971

Create a class that accept the callback as argument:

class MyClass:

    def __init__(self, on_connect=None):
        self._result = 0
        # store callback reference in a variable
        self._on_connect = on_connect

    def connect(self):
        self._result = 1
        # if callback is defined and it is a function/method
        if self._on_connect and callable(self._on_connect):
            # Send the object instance to the callback, 
            # you may use the same callback for multiple objects.
            self._on_connect(self)

    def get_result(self):
        return self._result

Then:

import MyClass

def on_connect_callback(instance):
    print('Connected with result code {}'.format(
        instance.get_result()))

my_obj = MyClass(on_connect=on_connect_callback)
my_obj.connect()

Upvotes: 2

h4z3
h4z3

Reputation: 5458

Let's add handlers to the class, with nice add method and general fire that calls the callbacks:

class myClass:
    def __init__(self):
        self.__result = 0
        self.on_connect = []

    def connect(self):
        self.__result = 1
        self.fire()

    def add_listener(self, listener):
        self.on_connect.append(listener)

    def fire(self):
        for listener in self.on_connect:
            listener(self.__result)

Then we only need to redo one thing in your main code - the way we add the listener. 

import myClass

def on_connect(result):
    print("Connected with result code "+result)

myclass = myClass()
myclass.add_listener(on_connect)

myclass.connect()

Upvotes: 2

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