Prerequisites – Python Class, Objects, Self Whenever object-oriented programming is done in Python, we mostly come across __init__ method in oops which we usually don’t fully understand. This article explains the main concept of __init__ but before understanding the __init__ some prerequisites are required.
What is __init__ in Python?
The Default __init__ Constructor in C++ and Java. Constructors are used to initializing the object’s state. The task of constructors is to initialize(assign values) to the data members of the class when an object of the class is created. Like methods, a constructor also contains a collection of statements(i.e. instructions) that are executed at the time of Object creation. It is run as soon as an object of a class is instantiated. The method is useful to do any initialization you want to do with your object.
Example:
Python3
# A Sample class with init methodclass Person: # init method or constructor def __init__(self, name): self.name = name # Sample Method def say_hi(self): print('Hello, my name is', self.name)p = Person('Nikhil')p.say_hi() |
Output:
Hello, my name is Nikhil
Understanding the code
In the above example, a person name Nikhil is created. While creating a person, “Nikhil” is passed as an argument, this argument will be passed to the __init__ method to initialize the object. The keyword self represents the instance of a class and binds the attributes with the given arguments. Similarly, many objects of the Person class can be created by passing different names as arguments. Below is the example of init in python with parameters
Example of __init__
Python3
# A Sample class with init methodclass Person: # init method or constructor def __init__(self, name): self.name = name # Sample Method def say_hi(self): print('Hello, my name is', self.name)# Creating different objectsp1 = Person('Nikhil')p2 = Person('Abhinav')p3 = Person('Anshul')p1.say_hi()p2.say_hi()p3.say_hi() |
Output:
Hello, my name is Nikhil Hello, my name is Abhinav Hello, my name is Anshul
__init__ with inheritance
Inheritance is the capability of one class to derive or inherit the properties from some other class. Let’s consider the below example to see how __init__ works in inheritance.
Python3
# Python program to# demonstrate init with# inheritanceclass A(object): def __init__(self, something): print("A init called") self.something = somethingclass B(A): def __init__(self, something): # Calling init of parent class A.__init__(self, something) print("B init called") self.something = somethingobj = B("Something") |
Output:
A init called B init called
So, the parent class constructor is called first. But in Python, it is not compulsory that the parent class constructor will always be called first. The order in which the __init__ method is called for a parent or a child class can be modified. This can simply be done by calling the parent class constructor after the body of the child class constructor.
Example:
Python3
# Python program to# demonstrate init with# inheritanceclass A(object): def __init__(self, something): print("A init called") self.something = somethingclass B(A): def __init__(self, something): print("B init called") self.something = something # Calling init of parent class A.__init__(self, something)obj = B("Something") |
Output:
B init called A init called
Note: To know more about inheritance click here.
