Introduction to classes

We will illustrate the concept of classes with an example of rational numbers, that is, numbers of the form q= q_N ⁄ q_D, where q_N and q_D are integers.

Figure 8.1: An example of a class declaration

We use rational numbers here only as an example for the class concept. For future work in Python with rational numbers use the fractions module (refer to [6]).

Class syntax

The definition of a class is made by a block command with the class keyword, the name of the class, and some statements in the block (refer to Figure 8.1):

class RationalNumber: 
      pass

An instance of this class (or in other words, an object of the type RationalNumber) is created by

r = RationalNumber()

and a query type(a) returns the answer,  <class'__main__.RationalNumber'>. If we want to investigate whether an object is an instance of this class, we can use this:

if isinstance(a, RationalNumber):
    print('Indeed it belongs to the class RationalNumber')  

So far we've generated an object...