__init__ in Python

__init__ method in Python is a constructor. It runs automatically 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.

1. __init__ with Parameters

You can pass multiple parameters to set up different attributes.

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

p1 = Person("Alice", 30)
p2 = Person("Bob", 25)

print(p1.name, p1.age)  # Alice 30
print(p2.name, p2.age)  # Bob 25

Alice 30
Bob 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.

2. Default Parameters in __init__

Like normal functions, you can use default values in constructors.

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

d1 = Dog("Buddy")
d2 = Dog("Max", "Golden Retriever", 5)
print(d1.name, d1.breed, d1.age)  
print(d2.name, d2.breed, d2.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.

3.__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 looks for B.__init__.
• Inside B.__init__, the line super().__init__() calls the parent’s (A) constructor.
• So "A init called" is printed first.
• Then the rest of B.__init__ runs, printing "B init called".

Related Article

• OOPs
• Inheritance