Constructors in Python

Difficulty Level : Basic
Last Updated : 19 Apr, 2020

Prerequisites : Object Oriented Programming in Python, Object Oriented Programming in Python | Set 2
Constructors are generally used for instantiating an object.The task of constructors is to initialize(assign values) to the data members of the class when an object of class is created.In Python the __init__() method is called the constructor and is always called when an object is created.

Syntax of constructor declaration :

def __init__(self):
    # body of the constructor

Types of constructors :

default constructor :The default constructor is simple constructor which doesn’t accept any arguments.It’s definition has only one argument which is a reference to the instance being constructed.
parameterized constructor :constructor with parameters is known as parameterized constructor.The parameterized constructor take its first argument as a reference to the instance being constructed known as self and the rest of the arguments are provided by the programmer.

Example of default constructor :

class GeekforGeeks: 
  
    # default constructor 
    def __init__(self): 
        self.geek = "GeekforGeeks"
  
    # a method for printing data members 
    def print_Geek(self): 
        print(self.geek) 
  
  
# creating object of the class 
obj = GeekforGeeks() 
  
# calling the instance method using the object obj 
obj.print_Geek() 

Output :

GeekforGeeks

Example of parameterized constructor :

class Addition: 
    first = 0
    second = 0
    answer = 0
      
    # parameterized constructor 
    def __init__(self, f, s): 
        self.first = f 
        self.second = s 
      
    def display(self): 
        print("First number = " + str(self.first)) 
        print("Second number = " + str(self.second)) 
        print("Addition of two numbers = " + str(self.answer)) 
  
    def calculate(self): 
        self.answer = self.first + self.second 
  
# creating object of the class 
# this will invoke parameterized constructor 
obj = Addition(1000, 2000) 
  
# perform Addition 
obj.calculate() 
  
# display result 
obj.display() 

Output :

First number = 1000
Second number = 2000
Addition of two numbers = 3000

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