__init__() method is a constructor which is automatically called when a new object of a class is created. Its main purpose is to initialize the object’s attributes and set up its initial state. When an object is created, memory is allocated for it and __init__ helps organize that memory by assigning values to attributes.

Let’s look at some examples.

__init__() with Parameters

You can pass parameters to initialize multiple attributes.

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

a = Person("Max", 30)
b = Person("Emilia", 25)

print(a.name, a.age) 
print(b.name, b.age)  

Max 30
Emilia 25

Explanation:

• self: refers to the current object (always the first parameter).
• name and age: parameters passed when creating the object.
• self.name and self.age: object attributes that store these values.

Default Parameters in __init__()

Like regular functions, __init__() can have parameters with default values.

class Dog:
    def __init__(self, name, breed="Mixed", age=1):
        self.name = name
        self.breed = breed
        self.age = age

a = Dog("Buddy")
b = Dog("Max", "Golden Retriever", 5)

print(a.name, a.breed, a.age)  
print(b.name, b.breed, b.age)  

Buddy Mixed 1
Max Golden Retriever 5

Explanation:

• breed="Mixed" and age=1 are default values.
• When creating Dog("Buddy"), Python uses the defaults, breed = "Mixed", age = 1.
• When creating Dog ("Max", "Golden Retriever", 5), the defaults are overwritten by the provided values.

__init__() Method with Inheritance

When using inheritance, both parent and child classes can have __init__() methods.

class A:
    def __init__(self):
        print("A init called")

class B(A):
    def __init__(self):
        super().__init__()   # Call parent __init__
        print("B init called")

obj = B()

A init called
B init called

Explanation:

• When obj = B() is created, Python first calls B.__init__(). Inside B.__init__, the line super().__init__() calls the parent’s (A) constructor.
• As a result, "A init called" is printed first.
• After the parent class initialization completes, remaining code in B.__init__() executes and "B init called" is printed.

Related Articles:

• OOPs
• Inheritance