Custom middleware creation in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is middleware in Flask?

Middleware in Flask is a piece of code that runs before or after the main request handler. It can modify requests or responses, like a helpful assistant checking or changing things as they pass through.

intermediate

How do you create custom middleware in Flask?

You create a class with a __call__ method that takes the WSGI environment and start_response function. Inside, you can add your code before or after calling the next app in the chain.

intermediate

What does the __call__ method do in Flask middleware?

The __call__ method makes the middleware class behave like a function. Flask calls it with request details, letting your middleware process or change the request or response.

beginner

Why use middleware in a Flask app?

Middleware helps add features like logging, authentication, or modifying requests without changing your main app code. It keeps your app clean and organized.

intermediate

How do you add your custom middleware to a Flask app?

Wrap your Flask app with your middleware class when creating the app. For example, app.wsgi_app = YourMiddleware(app.wsgi_app). This tells Flask to use your middleware.

What method must a Flask middleware class implement to be callable?

A handle

B __call__

C run

D __init__

The __call__ method allows the middleware class to be called like a function by Flask.

Where do you insert your middleware in a Flask app?

A Wrap the app's wsgi_app attribute

B Inside the route functions

C In the app.config dictionary

D In the templates folder

Middleware wraps the app's wsgi_app attribute to intercept requests and responses.

What can middleware modify in Flask?

A HTML templates

B Database schema

C Requests and responses

D Static files

Middleware can modify the incoming requests or outgoing responses.

Which of these is NOT a typical use of middleware?

A Modifying headers

B Authenticating users

C Logging requests

D Rendering HTML templates

Rendering HTML templates is done in route handlers, not middleware.

What arguments does the __call__ method in Flask middleware receive?

A environ and start_response

B request and response

C app and config

D self and app

The __call__ method receives the WSGI environ dictionary and start_response function.

Explain how to create and add custom middleware to a Flask app.

Think about how middleware acts like a filter around your app.

Describe three common uses of middleware in Flask applications.

Middleware helps with tasks before or after your main app runs.