What is difference between self and __init__ methods in python Class?

In Python classes, self and __init__ serve different but complementary purposes. Understanding their roles is essential for object-oriented programming in Python.

What is self?

The self parameter represents the instance of a class. It allows you to access the attributes and methods of the class from within its methods. When you call a method on an object, Python automatically passes the object itself as the first argument.

Example

class Student:
    def set_name(self, name):
        self.name = name  # self refers to the current instance
    
    def get_name(self):
        return self.name  # self accesses the instance attribute

student1 = Student()
student1.set_name("Alice")
print(student1.get_name())

Alice

What is __init__ method?

The __init__ method is a special method called a constructor. It is automatically called when an object is created from a class and allows you to initialize the attributes of the class with specific values.

Example

class Student:
    def __init__(self, name, age):
        self.name = name  # Initialize name attribute
        self.age = age    # Initialize age attribute
    
    def display_info(self):
        return f"Name: {self.name}, Age: {self.age}"

student1 = Student("Bob", 20)
print(student1.display_info())

Name: Bob, Age: 20

Practical Example

Let's find the cost of a rectangular field with breadth (120), length (160), costing 2000 rupees per square unit ?

class Rectangle:
    def __init__(self, length, breadth, unit_cost=0):
        self.length = length
        self.breadth = breadth
        self.unit_cost = unit_cost
    
    def get_area(self):
        return self.length * self.breadth
    
    def calculate_cost(self):
        area = self.get_area()
        return area * self.unit_cost

# Create rectangle: breadth=120, length=160, cost=2000 per sq unit
r = Rectangle(160, 120, 2000)
print("Area of Rectangle: %s sq units" % (r.get_area()))
print("Cost of rectangular field: Rs.%s" % (r.calculate_cost()))

Area of Rectangle: 19200 sq units
Cost of rectangular field: Rs.38400000

Key Differences

Conclusion

self is a reference to the current instance used in all methods, while __init__ is a constructor method that initializes object attributes. Both work together to create and manage objects in Python classes.