Class method vs Static method in Python

What is Class Method in Python? 

The @classmethod decorator is a built-in function decorator that is an expression that gets evaluated after your function is defined. The result of that evaluation shadows your function definition. A class method receives the class as an implicit first argument, just like an instance method receives the instance 

Syntax Python Class Method: 

class C(object):
    @classmethod
    def fun(cls, arg1, arg2, ...):
       ....
fun: function that needs to be converted into a class method
returns: a class method for function.

• A class method is a method that is bound to the class and not the object of the class.
• They have the access to the state of the class as it takes a class parameter that points to the class and not the object instance.
• It can modify a class state that would apply across all the instances of the class. For example, it can modify a class variable that will be applicable to all the instances.

What is the Static Method in Python?

A static method does not receive an implicit first argument. A static method is also a method that is bound to the class and not the object of the class. This method can’t access or modify the class state. It is present in a class because it makes sense for the method to be present in class.

Syntax Python Static Method: 

class C(object):
    @staticmethod
    def fun(arg1, arg2, ...):
        ...
returns: a static method for function fun.

Class method vs Static Method

The difference between the Class method and the static method is:

• A class method takes cls as the first parameter while a static method needs no specific parameters.
• A class method can access or modify the class state while a static method can’t access or modify it.
• In general, static methods know nothing about the class state. They are utility-type methods that take some parameters and work upon those parameters. On the other hand class methods must have class as a parameter.
• We use @classmethod decorator in python to create a class method and we use @staticmethod decorator to create a static method in python.

When to use the class or static method?

• We generally use the class method to create factory methods. Factory methods return class objects ( similar to a constructor ) for different use cases.
• We generally use static methods to create utility functions.

How to define a class method and a static method?

To define a class method in python, we use @classmethod decorator, and to define a static method we use @staticmethod decorator. 
Let us look at an example to understand the difference between both of them. Let us say we want to create a class Person. Now, python doesn’t support method overloading like C++ or Java so we use class methods to create factory methods. In the below example we use a class method to create a person object from birth year.

As explained above we use static methods to create utility functions. In the below example we use a static method to check if a person is an adult or not. 

Below is the complete Implementation 

• Python3

# Python program to demonstrate # use of class method and static method. from datetime import date     class Person:     def __init__(self, name, age):         self.name = name         self.age = age       # a class method to create a Person object by birth year.     @classmethod     def fromBirthYear(cls, name, year):         return cls(name, date.today().year - year)       # a static method to check if a Person is adult or not.     @staticmethod     def isAdult(age):         return age > 18     person1 = Person('mayank', 21) person2 = Person.fromBirthYear('mayank', 1996)   print(person1.age) print(person2.age)   # print the result print(Person.isAdult(22))

Output:

21
25
True

Auxiliary Space: O(1)