Instance vs Class Variables

In Object-Oriented Programming (OOP), variables inside a class are mainly of two types:

• Instance Variables
• Class Variables

Understanding the difference is very important for writing clean and structured programs.

1. Instance Variables

Instance variables belong to a specific object.
Each object has its own separate copy of instance variables.

They are usually defined inside the constructor using self.

Example

class Student:
    def __init__(self, name):
        self.name = name   # Instance variables1 = Student("Hira")
s2 = Student("Ali")print(s1.name)
print(s2.name)

Output:

Hira
Ali

Here:

• s1 and s2 have their own separate name
• Changing one object does not affect the other

Key Points

• Defined using self
• Created when object is created
• Unique for each object

2. Class Variables

Class variables belong to the class itself, not to individual objects.
All objects share the same class variable.

They are defined inside the class but outside the constructor.

Example

class Student:
    school = "GIGZ Academy"   # Class variable    def __init__(self, name):
        self.name = names1 = Student("Hira")
s2 = Student("Ali")print(s1.school)
print(s2.school)

Output:

GIGZ Academy
GIGZ Academy

Both objects share the same school value.

Changing Class Variable

Student.school = "W3Skillset"print(s1.school)
print(s2.school)

Now both objects will show the updated value.

Difference Between Instance and Class Variables

Instance Variable
Belongs to object
Separate copy for each object
Defined using self
Created when object is created

Class Variable
Belongs to class
Shared by all objects
Defined directly inside class
Created when class is defined

When to Use Which?

Use Instance Variables when:

• Data is different for each object
• Example: name, age, salary

Use Class Variables when:

• Data is common for all objects
• Example: school name, company name, tax rate

Final Understanding

Instance variables store object-specific data.
Class variables store shared data for all objects of the class.

Both are essential for writing efficient and well-structured OOP programs.