Classmethod() in Python

Python has a built-in function called classmethod() that gives a class method of the specified function.;

Syntax:

Parameter: This method accepts the name of the function as its parameter.

Return Type: This method returns the function converted to a class method.

We can also use the decorator form @classmethod for defining the classmethod.

Syntax:

@classmethod<
def function(cls, arg1, arg2, arg3...):

Where,

function: this is the function that is required to be converted to a class method

returns: the converted class method of the function.

Instead of being tied to an instance, classmethod() functions are attached to classes. Both classes and objects are capable of calling class methods. Both classes and objects can be used to invoke these methods.

Class method vs. Static Method

Although a static method requires no particular arguments, a class method accepts cls as its first argument.

Though a static method cannot access or alter the class state, a class method may.

Static methods are typically unaware of the class state. They are utility methods that operate on some parameters after receiving them. On the other hand, the class must be a parameter for class methods.

Python's @classmethod decorator and @staticmethod decorator are used to generate class and static methods, respectively.

Examples of classmethod in Python

This example will show how to create a simple classmethod.

In this illustration, we'll learn how to construct a class method. To do this, we made a class called Python with a variable called the course and a method called algo that prints the object that is passed to it.

We then called the class function algo without constructing a function object after passing the method Python.algo into the classmethod, which transforms the method into the class method.

Code

# Python program to show how to create a simple classmethod function

# Defining a function
class Python:
    course = 'Algorithm'
 
    def algo(object_):
        print("This is an algorithm: ", object_.course)
 
# Creating a classmethod function by passing a method to it
Python.algo = classmethod(Python.algo)
Python.algo()

Output

This is an algorithm:  Algorithm

Creating a class method using the classmethod() function

Code

# Python program to show how to create a classmethod function

# Creating a class 
class Names:
 
    # creating a variable
    name = "Javatpoint"
    # creating a method
    def print_name(object_):
        print("The given name is: ", object_.name)
# Before writing this line, print_name(), make the print name classmethod. It can only be called with an object, not the class.
Names.print_name = classmethod(Names.print_name)
 
# Now the print_name method can be called a classmethod
Names.print_name()

Output

The given name is:  Javatpoint

Factory Method Using Class Method

Factory design patterns use the classmethod() function when invoking several functions using the class name instead of the object.

Code

# Python program to show the use of a class method and a static method

# Importing the required library
from datetime import date
 
# Creating a class
class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age
 
    # Using the class method decorator to make the years of alumni class a class method class
    # Creating a class method.
    @classmethod
    def alumniYear(cls, name, year):
        return cls(name, date.today().year - year)
    # Creating a static method to check whether the student is an adult or not
    @staticmethod
    def isAdult(age):
        return age > 21

# Creating an instance of the class
person1 = Student('Harry', 22)
person2 = Student.alumniYear('Louis', 1999)
 
print(person1.age)
print(person2.age)
 
# print the result
print(Student.isAdult(22))

Output