Before_request hooks in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a before_request hook in Flask?

A before_request hook is a function that runs before each request is processed. It lets you run code like checking user login or setting up data before the main view runs.

beginner

How do you register a before_request function in Flask?

You use the @app.before_request decorator above a function. Flask calls this function before every request automatically.

intermediate

Can a before_request function stop a request from continuing?

Yes. If the before_request function returns a response (like a redirect or error), Flask stops and sends that response immediately, skipping the view function.

beginner

Why use before_request hooks instead of putting code inside each view?

They help avoid repeating code in every view. For example, checking if a user is logged in or setting up common data can be done once in a before_request hook.

intermediate

What happens if multiple before_request functions are registered?

Flask runs all before_request functions in the order they were registered. If any returns a response, the rest are skipped.

What decorator do you use to create a before_request hook in Flask?

A @app.after_request

B @app.teardown_request

C @app.route

D @app.before_request

The @app.before_request decorator registers a function to run before each request.

What happens if a before_request function returns a response?

A The response is sent immediately, skipping the view function.

B The response is ignored and the view runs anyway.

C Flask raises an error.

D The response is logged but the view runs.

Returning a response in before_request stops further processing and sends that response.

Which of these is a common use for before_request hooks?

A Serving static files

B Rendering HTML templates

C Checking if a user is logged in

D Handling form submissions

before_request hooks are often used to check user login status before views run.

If you register multiple before_request functions, in what order do they run?

A In reverse order

B In the order they were registered

C Random order

D Alphabetical order by function name

Flask runs before_request functions in the order they were added.

Can before_request hooks access the request data?

A Yes, they can access request data like headers and form inputs

B No, request data is not available yet

C Only URL parameters are accessible

D Only after the view runs

before_request hooks run after Flask receives the request, so they can access all request data.

Explain what a before_request hook is and how it affects the request flow in Flask.

Think about what happens before your page loads.

Describe a practical example where using a before_request hook improves your Flask app.

Imagine you want to protect many pages from unauthorized access.