A Byte of Python

Chapter 11. Object-Oriented Programming

Table of Contents

The self
Creating a Class
object Methods
Using Object Methds
The __init__ method
Using the __init__ method
Class and Object Variables
Using Class and Object Variables
Using Inheritance


In all our programs till now, we have designed our program around functions or blocks of statements which manipulate data. This is called the procedure-oriented way of programming. There is another way of organizing your program which is to combine data and functionality and wrap it inside what is called an object. This is called the object oriented programming paradigm. Most of the time you can use procedural programming but sometimes when you want to write large programs or have a solution that is better suited to it, you can use object oriented programming techniques.

Classes and objects are the two main aspecs of object oriented programming. A class creates a new type where objects are instances of the class. An analogy is that you can have variables of type int which translates to saying that variables that store integers are variables which are instances (objects) of the int class.

Note for C/C++/Java/C# Programmers

Note that even integers are treated as objects (of the int class). This is unlike C++ and Java (before version 1.5) where integers are primitive native types. See help(int) for more details on the class.

C# and Java 1.5 programmers will be familiar with this concept since it is similar to the boxing and unboxing concept.

Objects can store data using ordinary variables that belong to the object. Variables that belong to an object or class are called as fields. Objects can also have functionality by using functions that belong to a class. Such functions are called methods of the class. This terminology is important because it helps us to differentiate between functions and variables which are separate by itself and those which belong to a class or object. Collectively, the fields and methods can be referred to as the attributes of that class.

Fields are of two types - they can belong to each instance/object of the class or they can belong to the class itself. They are called instance variables and class variables respectively.

A class is created using the class keyword. The fields and methods of the class are listed in an indented block.