4 Python Custom exceptions

1. What is a Custom Exception?

A custom exception is an error that you create yourself.

In simple words:
👉 Python has many built-in errors
👉 Sometimes we need our own error message
👉 Custom exceptions help us control errors better

2. Why Use Custom Exceptions?

We use custom exceptions to:

• Show clear error messages

• Handle special rules in our program

• Make code easy to understand

3. Simple Custom Exception Example

We create a custom exception using a class.

Example

4. Custom Exception in Real Use

Example: Age Check

5. Handling Custom Exception with try-except

Example

6. Custom Exception Inside Function

Example

7. Custom Exception with Message

Example

8. When Should You Use Custom Exceptions?

Use custom exceptions when:
✔ Built-in exceptions are not enough
✔ You want custom messages
✔ Your program has specific rules

9. Common Beginner Mistakes

❌ Not Inheriting from Exception

❌ Wrong.

✔ Correct:

❌ Raising Exception Without try-except

👉 Program crashes.

10. Simple Practice Examples

Example 1: Password Check

Example 2: Marks Validation

Example 3: Custom Exception Function

11. Summary (Python Custom Exceptions)

✔ Custom exceptions are user-defined errors
✔ Created using class
✔ Must inherit from Exception
✔ Makes error handling clean
✔ Useful in real applications

📘 Perfect for Beginner eBook

This chapter is ideal for:

• Python beginner books

• School & college students

• Self-learners

If you want next, I can write:

• Python Debugging

• Logging

• Advanced File Handling

• Mini Python Projects

Just tell me 😊