Python 3 Object-Oriented Programming - Third Edition

Using functions as attributes

One of the interesting effects of functions being objects is that they can be set as callable attributes on other objects. It is possible to add or change a function to an instantiated object, demonstrated as follows:

class A: 
    def print(self): 
        print("my class is A") 
 
def fake_print(): 
    print("my class is not A") 
 
a = A() 
a.print() 
a.print = fake_print 
a.print() 

This code creates a very simple class with a print method that doesn't tell us anything we didn't know. Then, we create a new function that tells us something we don't believe.

When we call print on an instance of the A class, it behaves as expected. If we then set the print method to point at a new function, it tells us something different:

my class is ...