Example of classmethod in Python
Create a simple classmethod
In this example, we are going to see how to create a class method in Python. For this, we created a class named “Geeks” with a member variable “course” and created a function named “purchase” which prints the object. Now, we passed the method Geeks.purchase into a class method using the @classmethod decorator, which converts the method to a class method. With the class method in place, we can call the function “purchase” without creating a function object, directly using the class name “Geeks.”
Python3
class geeks: course = 'DSA' def purchase(obj): print("Purchase course : ", obj.course)geeks.purchase = classmethod(geeks.purchase)geeks.purchase() |
Purchase course : DSA
Create class method using classmethod()
Created print_name classmethod before creating this line print_name() It can be called only with an object not with the class now this method can be called as classmethod print_name() method is called a class method.
Python3
class Student: # create a variable name = "w3wiki" # create a function def print_name(obj): print("The name is : ", obj.name)# create print_name classmethod# before creating this line print_name()# It can be called only with object not with classStudent.print_name = classmethod(Student.print_name)# now this method can be called as classmethod# print_name() method is called a class methodStudent.print_name() |
The name is : w3wiki
Factory method using a Class method
Uses of classmethod() function are used in factory design patterns where we want to call many functions with the class name rather than an object.
Python3
# Python program to demonstrate# use of a class method and static method.from datetime import dateclass 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) def display(self): print("Name : ", self.name, "Age : ", self.age)person = Person('mayank', 21)person.display() |
Name : mayank Age : 21
How the class method works for the inheritance?
In this example, we are making Python class hierarchy with two classes, Person and Man, and demonstrates the usage of class methods and inheritance.
Python3
from datetime import date# random Personclass Person: def __init__(self, name, age): self.name = name self.age = age @staticmethod def from_FathersAge(name, fatherAge, fatherPersonAgeDiff): return Person(name, date.today().year - fatherAge + fatherPersonAgeDiff) @classmethod def from_BirthYear(cls, name, birthYear): return cls(name, date.today().year - birthYear) def display(self): print(self.name + "'s age is: " + str(self.age))class Man(Person): sex = 'Female'man = Man.from_BirthYear('John', 1985)print(isinstance(man, Man))man1 = Man.from_FathersAge('John', 1965, 20)print(isinstance(man1, Man)) |
True False
classmethod() in Python
The classmethod() is an inbuilt function in Python, which returns a class method for a given function.