How to write a simple callback function?

Question

Python 2.7.10

I wrote the following code to test a simple callback function.

def callback(a, b):
    print(\'Sum = {0}\'.format(a+b))

def main(         


        

Answer 1

The problem is that you're evaluating the callback before you pass it as a callable. One flexible way to solve the problem would be this:

def callback1(a, b):
    print('Sum = {0}'.format(a+b))

def callback2(a):
    print('Square = {0}'.format(a**2))

def callback3():
    print('Hello, world!')

def main(callback=None, cargs=()):
    print('Calling callback.')
    if callback != None:
        callback(*cargs)

main(callback1, cargs=(1, 2))
main(callback2, cargs=(2,))
main(callback3)

Optionally you may want to include a way to support keyword arguments.