Extending built-in exceptions in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of extending built-in exceptions in Python?

Extending built-in exceptions allows you to create custom error types that behave like standard errors but can carry specific information or handle special cases in your program.

beginner

How do you define a custom exception by extending a built-in exception?

You create a new class that inherits from a built-in exception class like Exception or ValueError, for example: <pre>class MyError(Exception):
    pass</pre>

intermediate

Why might you want to add an __init__ method to your custom exception?

Adding an __init__ method lets you store extra information about the error, like a message or error code, which can be accessed when handling the exception.

intermediate

What does the following code do?<br><pre>class MyError(Exception):
    def __init__(self, message, code):
        super().__init__(message)
        self.code = code</pre>

It defines a custom exception MyError that takes a message and a code. The message is passed to the base Exception class, and the code is stored as an attribute for extra error info.

beginner

How do you raise and catch a custom exception?

You use the raise keyword to throw the exception and a try-except block to catch it:<br>

try:
    raise MyError('Oops', 404)
except MyError as e:
    print(f'Error: {e}, code: {e.code}')

Which built-in class should you usually inherit from to create a custom exception?

A Exception

B object

C int

D list

Custom exceptions should inherit from Exception or one of its subclasses to behave like standard errors.

What does the super() function do in a custom exception's __init__ method?

A Creates a new exception

B Calls the parent class's __init__ method

C Raises the exception

D Prints the error message

super() calls the parent class's __init__ to properly initialize the base Exception part.

How can you add extra information to a custom exception?

A By using global variables

B By changing the built-in Exception class

C By raising multiple exceptions

D By defining additional attributes in the class

You add extra attributes in your custom exception class to store additional error details.

What happens if you raise a custom exception but do not catch it?

A The program continues silently

B The exception is ignored

C The program stops and shows a traceback

D The exception is converted to a string

Uncaught exceptions stop the program and print an error traceback.

Which keyword is used to raise a custom exception?

A raise

B throw

C catch

D try

The raise keyword is used to throw exceptions in Python.

Explain how to create and use a custom exception in Python.

Think about making a new class and how to handle errors.

Why is it useful to extend built-in exceptions instead of using Exception directly?

Consider how different errors help you understand problems better.