What is __init__ in Python

New Python developers who have a knowledge of Java or C++ finds this topic a little bit confusing because constructor in other programming languages has a same name as that of a class but in Python constructor is declared using __init__ method. __init__ is one of the magic methods that is defined inside a class and is called automatically when an instance of a class is created. It is sometimes known as dunder-init. It is used to initialize the instance variables. It takes default, keyworded and non-keyworded variable-length arguments.

Syntax of __init__

There are four different ways of declaring __init__ in Python-

def __init__(self, param1, param2, ..., paramn):
#__init__ method with default argument
def __init__(self, param1='defaultvalue1', param2, ..., paramn):
#__init__ method with non-keyworded variable-length argument
def __init__(self, *args):
#__init__ method with keyworded variable-length argument
def __init__(self, **kwargs):

Note:- A class should have atmost one __init__ method. If __init__ is not defined by you in a class then Python Interpreter will generate __init__() method that has an empty body. When you define more than one __init__ inside a class then only the last defined __init__ will be called when you create an object.
It is mandatory to specify self parameter to __init__

#Student class having __init__ with default argument
class Student:
	def __init__(self, name, standard='sixth'):
		self.name = name
		self.standard = standard

	def display(self):
		print('Student Name:', self.name)
		print('Studies in', self.standard)

s2 = Student('Geeta Sahu', 'tenth')
s2 = Student('Mohit Natani')


Student Name: Geeta Sahu
Studies in tenth
Student Name: Mohit Natani
Studies in sixth
#Car class having __init__ with default argument
class Car:
	def __init__(self, **kwargs):
		self.modelName = kwargs['modelName']
		self.modelYear = kwargs['modelYear']

	def display(self):
		print('Model Name:', self.modelName)
		print('Model Year:', self.modelYear)

c = Car(modelName='Jaguar F-Type', modelYear=2020)


Model Name: Jaguar F-Type
Model Year: 2020