A small example: A dice class

Before considering an extended example let's consider a small one to see what the syntactical elements are that support OOP in Python. In Python as in most OOP languages (including C++ and Java—but not Javascript) the key OOP construct is the class. A class specifies the characteristics of an object type and provides a rubber stamp or template for creating objects of a particular type. Consider for example a die (as in one dice, not death!). A die is quite a simple object. It has a single attribute, its number of sides, and just one method, roll, i.e. the only message you can really send a die is to roll itself and report the result. Like I said it's a simple object. Here is a complete importable module that defines a Die class and some code to test it (minimally). First the code alone (I have left out the docstrings to avoid obscuring the functional code):

# die_class_0.py
import random

class Die:
    def __init__(self, n):
        self.nsides = n
        
    def roll(self):
        spots = random.randint(1,self.nsides)
        return spots

if __name__ == '__main__':
    d1 = Die(6)
    red = Die(20)
    
    print 'Rolling d1 ...',
    result = d1.roll()
    print 'result =', result
    
    print 'Rolling red and d1 together gets you:', d1.roll() + red.roll()
    print 'The die d1 has %d sides' % (d1.nsides)

and then the code with (hopefully helpful) annotations,