Class Attributes vs Instance Attributes in Python

Class attributes are the variables defined directly in the class that are shared by all objects of the class.

Instance attributes are attributes or properties attached to an instance of a class. Instance attributes are defined in the constructor.

The following table lists the difference between class attribute and instance attribute:

Class Attribute Instance Attribute
Defined directly inside a class. Defined inside a constructor using the self parameter.
Shared across all objects. Specific to object.
Accessed using class name as well as using object with dot notation, e.g. classname.class_attribute or object.class_attribute Accessed using object dot notation e.g. object.instance_attribute
Changing value by using classname.class_attribute = value will be reflected to all the objects. Changing value of instance attribute will not be reflected to other objects.

The following example demonstrates the use of class attribute count.

class Student:
    count = 0
    def __init__(self):
        Student.count += 1                

In the above example, count is an attribute in the Student class. Whenever a new object is created, the value of count is incremented by 1. You can now access the count attribute after creating the objects, as shown below.

>>> std1=Student()
>>> Student.count
>>> std2 = Student()
>>> Student.count

The following demonstrates the instance attributes.

Example: Setting Attribute Values
class Student:
    def __init__(self, name, age): = name
        self.age = age

Now, you can specify the values while creating an instance, as shown below.

Example: Passing Instance Attribute Values in Constructor
>>> std = Student('Bill',25)
>>> std.age
>>> = 'Steve'
>>> std.age = 45
>>> std.age

Visit Python Class for more information.