Raising exceptions in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean to raise an exception in Python?

Raising an exception means telling Python that an error or unexpected situation happened. It stops normal code flow and looks for a way to handle the problem.

beginner

How do you raise a ValueError with a custom message in Python?

Use the raise keyword followed by the exception type and message, like this:<br>

raise ValueError("This is a custom error message")

beginner

What happens if you raise an exception but do not handle it?

If an exception is raised and not caught by any try-except block, the program stops running and shows an error message.

intermediate

Can you raise your own custom exception class in Python?

Yes! You can create a new class that inherits from <code>Exception</code> and then raise it like any other exception.

beginner

What is the purpose of raising exceptions in your code?

Raising exceptions helps you signal when something goes wrong, so you or other parts of the program can handle the problem properly instead of continuing with wrong data.

Which keyword is used to raise an exception in Python?

A raise

B throw

C error

D except

The correct keyword to raise an exception in Python is raise.

What will happen if you run this code?<br>

raise TypeError("Wrong type")

A The program ignores the error

B The program prints 'Wrong type' and continues

C Nothing happens

D The program stops and shows a TypeError with message 'Wrong type'

Raising an exception stops the program and shows the error message unless it is caught.

How do you raise a custom exception named MyError?

A raise Exception('MyError')

B throw MyError()

C raise MyError()

D error MyError()

You raise a custom exception by calling raise MyError().

Which of these is a correct way to raise a ValueError with message 'Invalid input'?

A throw ValueError('Invalid input')

B raise ValueError('Invalid input')

C raise 'Invalid input'

D error ValueError('Invalid input')

The correct syntax is raise ValueError('Invalid input').

If an exception is raised but not caught, what happens?

A Program stops and shows an error message

B Program restarts automatically

C Exception is ignored

D Program continues normally

Uncaught exceptions stop the program and display an error.

Explain in your own words what it means to raise an exception and why you might want to do it.

Think about telling your program something went wrong.

Write a short Python example that raises a ValueError with a message when a number is negative.

Use an if statement to check the number, then raise the error.