Custom error pages (404, 500) in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a custom 404 error page in a Flask app?

A custom 404 error page shows a friendly message when a user tries to visit a page that does not exist. It improves user experience by guiding them back to valid pages instead of showing a generic error.

beginner

How do you define a custom error handler for a 500 Internal Server Error in Flask?

Use the @app.errorhandler(500) decorator on a function that returns a response or template. This function runs when a server error happens, letting you show a custom message or page.

beginner

Which Flask function is used to render a custom error page template?

The render_template() function is used to load and show an HTML template for the error page, allowing you to design a nice layout and message.

intermediate

Why is it important to return the correct HTTP status code with a custom error page?

Returning the correct status code (like 404 or 500) helps browsers and search engines understand the error type. It also helps tools and users know the page is an error, not a normal page.

beginner

What happens if you don't define a custom error handler for 404 in Flask?

Flask shows a default plain text 404 error page. It works but looks basic and may confuse users. Custom pages improve clarity and keep your site style consistent.

Which decorator is used to create a custom 404 error page in Flask?

A @app.errorhandler(404)

B @app.route('/404')

C @app.handle_error(404)

D @app.custom_error(404)

The @app.errorhandler(404) decorator tells Flask to use the decorated function when a 404 error occurs.

What should a custom error handler function return?

A A rendered template and the error status code

B Only a string message

C Nothing, just print an error

D Redirect to homepage

The function should return a rendered template (HTML) and the correct HTTP status code to properly show the error page.

What HTTP status code is used for Internal Server Error?

A 404

B 500

C 403

D 200

500 is the standard HTTP status code for Internal Server Error.

If you want to show a custom page for any error, which decorator can you use?

A @app.route('/error')

B @app.errorhandler(404)

C @app.errorhandler(Exception)

D @app.catch_all()

Using @app.errorhandler(Exception) catches all exceptions and can be used to show a generic error page.

Why should custom error pages be user-friendly?

A To confuse users

B To hide errors completely

C To slow down the website

D To help users understand what went wrong and guide them

User-friendly error pages help users know what happened and how to continue, improving their experience.

Explain how to create a custom 404 error page in Flask and why it is useful.

Think about how Flask handles errors and how you can show a nicer page.

Describe the difference between default Flask error pages and custom error pages.

Consider what users see and how it affects their experience.