After_request hooks in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an after_request hook in Flask?

An after_request hook is a function that Flask runs after every request to modify or finalize the response before sending it to the client.

beginner

How do you register an after_request function in Flask?

You use the @app.after_request decorator above a function that takes the response object as a parameter and returns it, possibly modified.

beginner

What parameter does an after_request function receive?

It receives the response object that Flask created for the request, allowing you to change headers, cookies, or content before sending it.

intermediate

Can multiple after_request functions be used in a Flask app?

Yes, Flask runs all registered after_request functions in the order they were added, each receiving the response from the previous one.

beginner

Give a simple example of an after_request hook that adds a custom header.

Example:<br>

@app.after_request
 def add_header(response):
     response.headers['X-Custom-Header'] = 'Hello'
     return response

What does an after_request function in Flask modify?

A The database connection

B The incoming request data

C The Flask app configuration

D The response before it is sent to the client

An after_request function modifies the response object before Flask sends it back to the client.

Which decorator is used to register an after_request function?

A @app.after_request

B @app.before_request

C @app.route

D @app.teardown_request

The @app.after_request decorator registers a function to run after each request.

What must an after_request function always do with the response?

A Return the response object

B Modify the request object

C Close the Flask app

D Raise an exception

The function must return the response object, possibly modified, so Flask can send it to the client.

If multiple after_request functions exist, how are they executed?

A Only the first one runs

B They run in the order they were registered

C They run in reverse order

D They run simultaneously

Flask runs after_request functions in the order they were added, passing the response along.

Which of these is a valid use of an after_request hook?

A Modifying incoming form data

B Changing the URL route

C Logging response time

D Starting the Flask server

You can use after_request hooks to log info about the response, like timing or headers.

Explain what an after_request hook does in Flask and how you use it.

Think about what happens just before Flask sends data back to the browser.

Describe a practical example where an after_request hook would be useful.

Consider tasks that happen after your app creates a response but before the user sees it.