Object oriented programming in Python

Object-oriented programming is a powerful programming paradigm that allows you to break down complex problems into manageable parts, by creating and manipulating objects. In this tutorial, you will learn about various object properties such as class, methods, and inheritance, and how to create and use them in your Python programs. Whether you are a beginner or already familiar with Python programming, this tutorial will give you a solid foundation in object-oriented programming in Python. So let's dive in and explore the wonderful world of Object-Oriented Programming with Python!

Object oriented programming using Python

• In our OOPs concepts tutorial we have read that object is an instance of class.
  • i.e. to create an object, first we need to define a class.
  • Then from this class we can create multiple objects.
• Class is a template for defining an object.
• Every object of a class has :
  • state - defined by the data members of the class
  • behavior - defined by the data functions of the class
  • identity - every object of a class is different from other objects.
• Note # : 
  • Everything in Python is treated as an object, i.e be it variables,  constants,  functions,  data-types,  keywords,  operators etc. everything in python is an object of some class or the other.
  • Functions are treated as first class objects in python. This concept is used in advanced concepts like closures.

Defining a class in Python :

• In Python a class is defined by using the  class  keyword.
• The basic syntax of creating a class in Python is as follows : 

class Classname:
	# Body of the class
 	# Defining attributes and methods.
 
 

Defining a real class in Python :

• Below we have a real python code of defining an  Employee  class.
• The class first defines a class variable  company_address
• Then a constructor is defined to initialize the data members -
  • name 
  • id
  • desig
• Then two member functions are defined :
  • calculate_salary()
  • record_attendance()

class Employee:
	company_address = "12th street"

 	# state - initializing data members
 	def __init__(self, name, id, desig):
  		# data members (instance variables)
  		self.name = name
  		self.id = id
  		self.desig = desig
 	
 	# Behavior (instance methods)
 	def calculate_salary(self):
  		# Code to calculate salary
 	
 	# Behavior (instance methods)
 	def record_attendance(self):
  		# Code to record attendance
  
  

Creating an object of the class - Instantiating the class

• An instance of the class is created when we create a new object of the class.
• The basic syntax of creating a new object of a class is 
  •  object_name = Classname(data_member1, data_member2, data_member3,...) 
• In our previous example an object of the employee class can be created as :

steve = Employee('Steve', 1203, 'Project Manager')

Constructors in Python :

• The process of creating an object is divided into two parts : 
  • creating an object using the  __new__  method.
  • initializing the data members of the object using the  __init__  method.
• In Python a constructor is used to create and initialize an object of the class.
• A constructor is a special method of the class.
• We have a detailed tutorial on constructors in Python which explains all these concepts and different types of constructors in detail.

Class Attributes

• Class attributes can be of two types :
  • Instance variables
  • Class variables (or static variables)

Instance variables :

• instance variables are the data members attached to the instances of a class.
• instance variables are created using the constructor of the class.
• Every object has its own copy of instance variables.
• instance variables are accessed by dot notation using the object name :  object_name.instance_var_name 
• In the class defined in the previous section the instance variables are : 

name
id
desig

• To access the instance variables for the object created above we can use the following code  :

 emp_name = steve.name 
 emp_id = steve.id 
 emp_desig = steve.desig
 
 

Class Variables :

• Class variables are defined for the class itself.
• Class variables are not attached to any particular object.
• Class variables are shared by all objects of the class.
• The value of the class variables remain the same for all objects.
• Class variables are also known as static variables.
• Only one copy of class variables is created and all objects share this copy.
• class variables are accessed by dot notation using the class name :  class_name.class_var_name 
• In the class defined above  company_address  is a class variable :
  • the value of   company_address  will be the same for all the employees.
  • if the address of the company changes, it will change for all the employees.
• The class variable   company_address  can be accessed using the syntax :

adress = Employee.company_address

Methods of the Class

• In a python class we can have three types of Methods :
  • Instance methods
  • Class methods
  • Static methods

Instance Methods :

• Instance methods define the behavior of an object.
• A method is called instance method if it uses instance variables.
• An instance method can be used to modify the state of the object i.e. the data of the object.
• Instance methods are accessed by dot notation using the object name :  obj_name.instance_method() 
• In the class example shown above, the instance methods are :
  • calculate_salary()
  • record_attendance()
• To access these methods for object  steve  we can use the following syntax :

salary = steve.calculate_salary()

Class Methods :

• Class methods are used to access the class variables.
• These methods are not attached to any object.
• Class methods can be created in two ways :
  • using @classmethod decorator 
  • using the classmethod() function
• Both these methods are discussed in detail in our tutorial on class methods in python.
• class methods are accessed by dot notation using the class name :  class_name.class_method() 

Static methods :

• Static methods are generic utility methods.
• These are neither instance methods nor class methods.
• In other words these methods do not have access to instance and class variables.
• Static methods can be created in two ways :
  • using @staticmethod decorator 
  • using the staticmethod() function
• Both these methods are discussed in detail in our tutorial on static methods in python.
• static methods can be accessed :
  • using the class name and dot operator.
  • using the object name and dot operator.
• static methods are accessed by dot notation using the class name :  class_name.static_method() 

Properties

• In Python, properties are a way of controlling access to class attributes.
• Properties  can be used to execute the setter and getter methods of the class. 
  • The setter method is used to set the value of an attribute.
  • The getter method is used to retrieve the value of an attribute.
• We have a dedicated tutorial on the topic of properties in Python.