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Anubhav Sharma
Anubhav Sharma

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The Anubhav portal was launched in March 2015 at the behest of the Hon'ble Prime Minister for retiring government officials to leave a record of their experiences while in Govt service .

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1 Answers

Anubhav Sharma
Anubhav Sharma 26 Oct 2025
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In Python, class methods are special methods that are bound to the class (not the instance).
They can modify or access class-level data shared across all instances.

1. Definition

A class method is defined using the decorator:

@classmethod

and it takes cls as the first parameter (not self).

2. Syntax

class MyClass:
    class_variable = "Shared Value"

    @classmethod
    def my_class_method(cls, arg1):
        print("Class variable:", cls.class_variable)
        print("Argument:", arg1)

3. Usage Example

class Student:
    school_name = "Green Valley High"

    def __init__(self, name, age):
        self.name = name
        self.age = age

    @classmethod
    def change_school(cls, new_name):
        cls.school_name = new_name

# Before changing
print(Student.school_name)  # Green Valley High

# Change using class method
Student.change_school("Blue Ridge Academy")
print(Student.school_name)  # Blue Ridge Academy

Explanation:

  • change_school() is called on the class, not on an instance.
  • It modifies the class variable, and the change affects all instances.

4. Difference Between Instance, Class, and Static Methods

Method Type Decorator First Parameter Can Access Instance (self) Can Access Class (cls) Common Use
Instance Method (None) self Yes Via self.__class__ Works on instance data
Class Method @classmethod cls No Yes Modify class-level data
Static Method @staticmethod (none) No No Utility methods (no access to instance/class)

5. Example Showing All Three

class Example:
    count = 0

    def __init__(self):
        Example.count += 1

    def instance_method(self):
        return f"Instance method called. Instance count: {self.count}"

    @classmethod
    def class_method(cls):
        return f"Class method called. Total instances: {cls.count}"

    @staticmethod
    def static_method():
        return "Static method called. No instance or class data used."

Usage:

obj = Example()
print(obj.instance_method())
print(Example.class_method())
print(Example.static_method())
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