Python Instance variables

1. What is an Instance Variable?

An instance variable is a variable that belongs to one object only.

In simple words:
👉 Each object has its own data
👉 One object’s value does not affect another object
👉 Instance variables are defined using self

2. Why Use Instance Variables?

We use instance variables to:

• Store object-specific data

• Keep data separate for each object

• Avoid data conflict

3. Simple Instance Variable Example

Example

👉 p1 and p2 have different names.

4. Instance Variables vs Class Variables

Example

5. Change Instance Variable Value

Example

👉 Only s1 is changed.

6. Create Instance Variable Outside Constructor

Example

7. Instance Variables Inside Methods

Example

8. Delete Instance Variable

Example

9. Real-Life Example (Bank Account)

Example

10. Common Beginner Mistakes

❌ Forgetting self

❌ Wrong.

❌ Using Class Variable Instead of Instance Variable

👉 All objects share same value.

11. Simple Practice Examples

Example 1: Book Class

Example 2: Student Marks

Example 3: User Profile

12. Summary (Python Instance Variables)

✔ Instance variables belong to object
✔ Defined using self
✔ Each object has its own copy
✔ Can be changed per object
✔ Important OOP concept

📘 Perfect for Beginner eBook

This chapter is ideal for:

• Python beginner books

• School & college students

• Self-learners

If you want next, I can write:

• Class Variables

• Methods (Instance, Class, Static)

• Inheritance

• Real OOP Projects

Just tell me 😊