Python Class Methods

🐍 Python Class Methods

In Python, class methods are methods that operate on the class itself, not on instances (objects).
They are defined using the @classmethod decorator.

1️⃣ Key Points About Class Methods

Decorated with @classmethod.
First parameter is cls, which refers to the class, not the instance.
Can access class variables but cannot access instance variables directly.
Can be called on the class or on an instance.

2️⃣ Basic Syntax

class MyClass:
class_var = 0 @classmethod
def show_class_var(cls):
print("Class variable:", cls.class_var)

Call the method:



MyClass.show_class_var() # Class variable: 0


Or via object:



obj = MyClass()
obj.show_class_var() # Class variable: 0

class MyClass:

class_var = 0 @classmethod

def show_class_var(cls):

print("Class variable:", cls.class_var)

Call the method:

MyClass.show_class_var() # Class variable: 0

Or via object:

obj = MyClass()

obj.show_class_var() # Class variable: 0

3️⃣ Example: Incrementing a Class Variable

class Employee:
employee_count = 0 # class variabledef __init__(self, name):
self.name = name
Employee.employee_count += 1

@classmethod
def total_employees(cls):
print(f"Total Employees: {cls.employee_count}")

e1 = Employee("Vipul")
e2 = Employee("Riya")

class Employee:

employee_count = 0 # class variabledef __init__(self, name):

self.name = name

Employee.employee_count += 1

@classmethod

def total_employees(cls):

print(f"Total Employees: {cls.employee_count}")

e1 = Employee("Vipul")

e2 = Employee("Riya")

Employee.total_employees() # Total Employees: 2

4️⃣ Factory Method Using Class Method

Class methods can also be use as factory methods to create objects with alternative constructors.

class Person:
def __init__(self, name, age):
self.name = name
self.age = age @classmethod
def from_string(cls, data_str):
name, age = data_str.split("-")
return cls(name, int(age))

p1 = Person.from_string("Vipul-25")
print(p1.name) # Vipul
print(p1.age) # 25

class Person:

def __init__(self, name, age):

self.name = name

self.age = age @classmethod

def from_string(cls, data_str):

name, age = data_str.split("-")

return cls(name, int(age))

p1 = Person.from_string("Vipul-25")

print(p1.name) # Vipul

print(p1.age) # 25

5️⃣ Difference Between Instance Method and Class Method

Feature	Instance Method	Class Method
Decorator	None	`@classmethod`
First Parameter	`self` (object)	`cls` (class)
Access	Instance variables	Class variables
Call	On object only	On object or class

6️⃣ Class Method vs Static Method (Quick Comparison)

Feature	Class Method	Static Method
Decorator	`@classmethod`	`@staticmethod`
First Param	`cls`	None
Access	Class variables	Cannot access class or instance vars
Use	Factory methods, class-level logic	Utility functions

7️⃣ Real-World Example: Bank Account

class Bank:
bank_name = "ABC Bank"
accounts = 0def __init__(self, owner, balance):
self.owner = owner
self.balance = balance
Bank.accounts += 1

@classmethod
def bank_info(cls):
print(f"Bank: {cls.bank_name}, Total Accounts: {cls.accounts}")

b1 = Bank("Vipul", 5000)
b2 = Bank("Riya", 10000)

class Bank:

bank_name = "ABC Bank"

accounts = 0def __init__(self, owner, balance):

self.owner = owner

self.balance = balance

Bank.accounts += 1

@classmethod

def bank_info(cls):

print(f"Bank: {cls.bank_name}, Total Accounts: {cls.accounts}")

b1 = Bank("Vipul", 5000)

b2 = Bank("Riya", 10000)

Bank.bank_info() # Bank: ABC Bank, Total Accounts: 2

✅ Summary

Instance Method → works on object (self)
Class Method → works on class (cls)
Static Method → utility method, independent of object/class

Python Class Methods