Python - Class Attributes (Complete Guide for Beginners)

 In Python, class attributes are variables that belong to the class itself rather than individual objects. They are shared across all instances (objects) of the class.

Class attributes are useful when you want to store common data that should be the same for every object.

In this tutorial, you will learn what class attributes are, how to use them, and how they differ from instance attributes.

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What is a Class Attribute?

A class attribute is a variable defined inside a class but outside any method.

It is shared by all objects of that class.

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Creating a Class Attribute

Example:

class Student:
    school = "ABC School"  # Class attribute

print(Student.school)

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Accessing Class Attributes

You can access class attributes using:

• Class name
• Object name

Example:

class Student:
    school = "ABC School"

s1 = Student()

print(Student.school)
print(s1.school)

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Class Attribute Shared by All Objects

Example:

class Student:
    school = "ABC School"

s1 = Student()
s2 = Student()

print(s1.school)
print(s2.school)

Output:

ABC School
ABC School

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Modifying Class Attributes

You should modify class attributes using the class name.

Example:

class Student:
    school = "ABC School"

Student.school = "XYZ School"

print(Student.school)

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Class Attribute vs Instance Attribute

Class Attribute	Instance Attribute
Shared by all objects	Unique to each object
Defined in class body	Defined inside init
Access via class or object	Access via self

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Example: Both Together

class Student:
    school = "ABC School"  # Class attribute

    def __init__(self, name):
        self.name = name  # Instance attribute

s1 = Student("John")
s2 = Student("Alice")

print(s1.school, s1.name)
print(s2.school, s2.name)

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Changing Class Attribute via Object (Important Concept)

If you change class attribute using an object, it creates a new instance variable.

Example:

class Student:
    school = "ABC School"

s1 = Student()
s2 = Student()

s1.school = "New School"

print(s1.school)
print(s2.school)

Output:

New School
ABC School

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Why This Happens

• Student.school → class attribute
• s1.school = ... → creates instance attribute

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Real-World Example: School System

class Student:
    school = "Green Valley School"

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

s1 = Student("John")
s2 = Student("Sara")

print(s1.name, s1.school)
print(s2.name, s2.school)

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Real-World Example: Company System

class Employee:
    company = "Tech Corp"

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

e1 = Employee("Ali", "Developer")
e2 = Employee("Sara", "Designer")

print(e1.name, e1.company)
print(e2.name, e2.company)

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When to Use Class Attributes

Use class attributes when:

• Data is shared by all objects
• Values are constant or common
• Example: school name, company name, tax rate

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Common Mistakes

Mistake 1: Modifying via object

❌ Wrong:

s1.school = "New School"

✔ Creates instance attribute instead of changing class attribute

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Mistake 2: Confusing instance and class attributes

✔ Instance = unique data
✔ Class = shared data

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Mistake 3: Forgetting class name access

Student.school = "New Name"

✔ Correct way to update class attribute

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Safe Example

class Demo:
    value = 10

Demo.value = 20
print(Demo.value)

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Key Points Summary

• Class attributes are shared across all objects
• Defined inside class but outside methods
• Accessed using class name or object
• Changing via class affects all objects
• Changing via object creates instance attribute

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Conclusion

Class attributes are an important part of Python OOP that help you manage shared data efficiently.

You learned:

• What class attributes are
• How to create and access them
• Difference between class and instance attributes
• Real-world examples

Mastering class attributes helps you build cleaner and more efficient object-oriented programs.