12. Class Methods

What is a Class Method?

A class method is a method that works with the class itself rather than with individual objects.

Class methods are created using the @classmethod decorator.

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Example

class Student:

    school = "ABC School"

    @classmethod
    def get_school(cls):
        return cls.school

print(Student.get_school())

Output

ABC School

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What is a Class Variable?

school = "ABC School"

This is a class variable.

It belongs to the class itself.

Student.school

Output:

ABC School

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Understanding cls

In a class method:

@classmethod
def get_school(cls):

cls refers to the class.

Python internally does something similar to:

Student.get_school(Student)

Therefore:

cls = Student

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Understanding cls.school

Since:

cls = Student

Then:

cls.school

becomes:

Student.school

Output:

ABC School

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Visual Representation

Student Class
│
├── school = "ABC School"
│
└── get_school()

Calling:

Student.get_school()

makes:

cls
 │
 ▼
Student Class

Therefore:

cls.school

accesses:

Student.school

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Difference Between self and cls

self	cls
Refers to an object	Refers to a class
Used in instance methods	Used in class methods
Receives the current object	Receives the current class

Example:

def show(self):

@classmethod
def get_school(cls):

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Why Use Class Methods?

Class methods are useful when working with class variables.

Example:

class Student:

    school = "ABC School"

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

Usage:

Student.change_school("XYZ School")

Now:

print(Student.school)

Output:

XYZ School

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Real-Life Analogy

Imagine:

School
│
├── Name = ABC School
│
├── Student 1
├── Student 2
└── Student 3

The school name belongs to the school, not to any particular student.

A class method works with information that belongs to the class itself.

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Rule to Remember

• Use self when working with object data.
• Use cls when working with class data.
• Class methods are created using @classmethod.
• Class methods can access and modify class variables.