Constructors in Python

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 the 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 a simple constructor which doesn’t accept any arguments. Its 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 takes 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 :

Python3

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 the parameterized constructor :

Python3

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
obj1 = Addition(1000, 2000)

# creating second object of same class
obj2 = Addition(10, 20)

# perform Addition on obj1
obj1.calculate()

# perform Addition on obj2
obj2.calculate()

# display result of obj1
obj1.display()

# display result of obj2
obj2.display()

Output

First number = 1000
Second number = 2000
Addition of two numbers = 3000
First number = 10
Second number = 20
Addition of two numbers = 30