Use cases for each method type in Python

Introduction

Methods help organize code inside classes. Different method types serve different jobs to keep code clear and easy to use.

Use instance methods when you want to work with data unique to each object.

Use class methods when you need to change or access data shared by all objects of a class.

Use static methods when the task relates to the class but does not need any object or class data.

Syntax

Python

class ClassName:
    def instance_method(self, args):
        # works with object data
        pass

    @classmethod
    def class_method(cls, args):
        # works with class data
        pass

    @staticmethod
    def static_method(args):
        # independent function inside class
        pass

self refers to the object calling the method.

cls refers to the class itself, not an object.

Examples

Instance method bark uses object data name.

Python

class Dog:
    def __init__(self, name):
        self.name = name

    def bark(self):
        print(f"{self.name} says Woof!")

Class method get_species accesses shared class data species.

Python

class Dog:
    species = "Canis familiaris"

    @classmethod
    def get_species(cls):
        return cls.species

Static method is_dog checks something related but does not use object or class data.

Python

class Dog:
    @staticmethod
    def is_dog(animal):
        return animal.lower() == "dog"

Sample Program

This program shows all three method types working together in a class.

Python

class Car:
    wheels = 4  # class attribute

    def __init__(self, color):
        self.color = color  # instance attribute

    def paint(self, new_color):
        self.color = new_color  # instance method changes object data

    @classmethod
    def number_of_wheels(cls):
        return cls.wheels  # class method returns shared data

    @staticmethod
    def honk():
        print("Beep beep!")  # static method unrelated to object or class data

car1 = Car("red")
print(car1.color)  # red
car1.paint("blue")
print(car1.color)  # blue
print(Car.number_of_wheels())  # 4
Car.honk()

Important Notes

Instance methods always need self to access object data.

Class methods use cls to access or change class-wide data.

Static methods are like normal functions but kept inside the class for organization.

Summary

Instance methods work with data unique to each object.

Class methods work with data shared by all objects of the class.

Static methods perform tasks related to the class but don't use object or class data.