py

Methods

Class Method
Static Method

Class Method

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:

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.

Static Method

A static method does not receive an implicit first argument.

Syntax:

class C(object):
    @staticmethod
    def fun(arg1, arg2, ...):
        ...
returns: a static method for function fun.
A static method is also a method that is bound to the class and not the object of the class.
A static 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.

Class method vs Static Method

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 what?

We generally use 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.

Implementation

# 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