Exception hierarchy in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the base class for all exceptions in Python?

The base class for all exceptions in Python is <code>BaseException</code>. All other exceptions inherit from it.

beginner

Which class do most user-defined exceptions inherit from?

Most user-defined exceptions inherit from the <code>Exception</code> class, which is a subclass of <code>BaseException</code>.

intermediate

What is the difference between Exception and BaseException?

<code>BaseException</code> is the root of the exception hierarchy. <code>Exception</code> is a subclass used for most errors that programs should catch. Some exceptions like <code>SystemExit</code> and <code>KeyboardInterrupt</code> inherit directly from <code>BaseException</code> and are usually not caught by normal code.

intermediate

Name two exceptions that inherit directly from BaseException and are usually not caught by normal exception handlers.

Two exceptions that inherit directly from BaseException are SystemExit and KeyboardInterrupt. They are used to exit programs or interrupt execution and are usually not caught by normal except Exception blocks.

beginner

How does the exception hierarchy help in writing exception handling code?

The exception hierarchy allows you to catch broad categories of errors by catching a parent class like <code>Exception</code>, or catch specific errors by catching subclasses. This helps write flexible and clear error handling.

Which class is the root of all exceptions in Python?

A Error

B Exception

C StandardError

D BaseException

BaseException is the root class for all exceptions in Python.

Which exception is NOT a subclass of Exception?

A ValueError

B IndexError

C KeyboardInterrupt

D TypeError

KeyboardInterrupt inherits directly from BaseException, not Exception.

If you want to catch most errors in your program, which class should you catch?

A Exception

B KeyboardInterrupt

C SystemExit

D BaseException

Catching Exception will catch most program errors but not system-exiting exceptions.

Which exception is raised when a program is asked to exit?

A SystemExit

B RuntimeError

C ValueError

D Exception

SystemExit is raised when the program is asked to exit.

Why should you avoid catching BaseException directly?

A It does not catch any exceptions.

B It catches all exceptions including system-exiting ones, which can cause problems.

C It only catches syntax errors.

D It is deprecated.

Catching BaseException catches all exceptions including SystemExit and KeyboardInterrupt, which can interfere with program exit or interruption.

Explain the Python exception hierarchy starting from BaseException.

Think about which exceptions are caught normally and which are special.

Why is it important to understand the exception hierarchy when writing try-except blocks?

Consider how catching a parent class affects what errors you handle.