Summary  
This chapter explains how to create custom exception classes by inheriting from the built-in Exception, how to raise and catch them with try-except blocks, and how to add custom attributes for richer error information.

General domain of usage  
User input validation

**Video: Defining and Using Custom Exceptions in Python**

This video demonstrates how to create your own exception classes by subclassing the built-in `Exception` type, why custom exceptions are useful for application-specific error handling, and how to raise and catch them in practice.

Defining your own **custom exceptions** in Python allows you to handle application-specific errors in a clear and organized way. Custom exceptions make your code more readable and easier to debug, especially in complex systems where distinguishing between different error types is important. To define a custom exception, you create a new class that inherits from the built-in `Exception` class. This approach gives you access to all the standard exception behavior, while allowing you to add custom messages or attributes if needed.

A good practice is to name your custom exception classes using the `Error` suffix to make their purpose clear. By following this convention, you help anyone reading your code quickly recognize which classes are exceptions.

# Define a custom exception for invalid user input
class InvalidUserInputError(Exception):
    pass

def process_age(age):
    if age < 0:
        raise InvalidUserInputError("Age cannot be negative.")
    return f"User age is {age}"

try:
    print(process_age(-5))
except InvalidUserInputError as e:
    print(f"Custom Exception Caught: {e}")

What is the correct way to raise a custom exception in Python?

Which of the following is the best practice when naming your custom exception classes in Python?

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Defining Custom Exceptions

1. What is the correct way to raise a custom exception in Python?

2. Which of the following is the best practice when naming your custom exception classes in Python?