@classmethod Function Decorator

Python - classmethod Function Decorator

Python @classmethod is a function decorator that is used to specify a method as a class method.

There is a difference between class method and a regular method inside a class. A class method is a method that belongs to a class rather than an instance of a class.

In this tutorial, we will learn the syntax and usage of classmethod function decorator, with examples.

Syntax

The syntax of classmethod function decorator is

class SomeClassName:
    @classmethod
    def funcitonName():
        pass

Examples

1. Define a class method

In the following program, we will define a class A, and a class method in it named myFunction().

Python Program

class A:
    @classmethod
    def myFunction(self, msg) :
        print(msg)

# Calling on class
A.myFunction('Hello World!')

# Calling on class instance
A().myFunction('Hello User!')

Output

Hello World!
Hello User!

Uses of Class Method

The following are some of the common uses of class methods in Python.

  1. Factory methods: Class methods are commonly used to create objects of a class in a more flexible and convenient way. A class method can create an instance of the class with custom arguments and return it to the caller.
  2. Alternative constructors: Class methods can be used to define alternative ways of creating instances of a class. For example, a datetime class may have a fromtimestamp class method that creates a datetime object from a Unix timestamp.
  3. Encapsulation: Class methods can be used to encapsulate logic that operates on the class itself, rather than on its instances. For example, a BankAccount class may have a class method that calculates the total balance across all accounts.
  4. Inheritance: Class methods can be used to define methods that can be overridden by subclasses, providing a way to implement polymorphism in Python.
  5. Initialization: Class methods can be used to initialize class-level state or set up class-level configuration.

Summary

In this Built-in Functions tutorial, we learned the syntax of the object() built-in function, and how to use this function to create an empty object.