Python Class Vs Instance Variables

When working with Python classes, a common point of confusion is the difference between instance variables and class variables.

They may look similar, but they behave very differently.

In this short and clear guide for Python Class vs Instance Variables, we’ll break down:

Let’s begin.

🧍 What Is an Instance Variable?

An instance variable belongs to a specific object.

It is created inside the __init__() method using self:

Python

class Student:
    def __init__(self, name):
        self.name = name  # instance variable

Every time you create a new Student, it gets its own name.

Python

s1 = Student("Ali")
s2 = Student("Fatima")

print(s1.name)  # Ali
print(s2.name)  # Fatima

✅ Each object has its own copy of the variable.

A class variable is shared by all objects of the class.

It is defined outside of any method, directly inside the class.

Python

class Student:
    school = "PyUniverse"  # class variable

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

Now:

Python

s1 = Student("Ali")
s2 = Student("Fatima")

print(s1.school)  # PyUniverse
print(s2.school)  # PyUniverse

✅ Every object shares the same value unless it’s overridden.

Feature	Instance Variable	Class Variable
Scope	Specific to each object	Shared across all objects
Defined in	`__init__()` with `self.var`	Inside class, outside any method
Memory	Separate copy per object	One copy shared by class and all objs
Modified using	`self.var = value`	`ClassName.var = value` (preferred)

Python

s1.school = "AnotherSchool"

You might think this changes the class variable for all objects…

But it actually creates a new instance variable only for s1.

✅ To change it for all objects:

Python

Student.school = "AnotherSchool"

Class Variable = Common across all students (e.g., school name)
Instance Variable = Unique to each student (e.g., their name, roll number)