Global exception middleware in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of global exception middleware in FastAPI?

Global exception middleware catches errors that happen anywhere in the app, letting you handle them in one place and send friendly error messages to users.

beginner

How do you add global exception middleware in FastAPI?

You create a middleware function that catches exceptions, then add it to your FastAPI app using the @app.middleware decorator or add_middleware method.

intermediate

What is the role of the 'Request' and 'call_next' parameters in FastAPI middleware?

Request is the incoming user request. call_next is a function that runs the next step in the app and returns the response. Middleware can catch errors before or after calling call_next.

beginner

Why is it helpful to return JSON responses in global exception middleware?

Returning JSON keeps error messages consistent and easy to read for frontend apps or API users, improving user experience and debugging.

beginner

What happens if you don't use global exception middleware in a FastAPI app?

Errors might show default server messages or crash the app, confusing users and making debugging harder.

What decorator is commonly used to add middleware in FastAPI?

A @app.middleware

B @app.route

C @app.exception_handler

D @app.get

The @app.middleware decorator is used to add middleware functions that process requests and responses.

In FastAPI middleware, what does the 'call_next' function do?

A Stops the request

B Sends a response directly

C Calls the next middleware or route handler

D Raises an exception

call_next runs the next step in the request handling chain and returns the response.

Why use global exception middleware instead of try-except in each route?

A To handle errors in one place for all routes

B To slow down the app

C To avoid writing any error handling

D To make routes longer

Global middleware centralizes error handling, making code cleaner and consistent.

What type of response is best to return from global exception middleware in an API?

A Plain text

B JSON response

C HTML page

D Redirect

JSON responses are standard for APIs and easy for clients to parse.

Which exception is commonly caught in global exception middleware to handle unexpected errors?

A ValueError

B HTTPException

C KeyError

D Exception

Catching the base Exception class helps handle any unexpected error.

Explain how global exception middleware works in FastAPI and why it is useful.

Think about how middleware wraps around all requests and responses.

Describe the steps to create and add a global exception middleware in a FastAPI app.

Focus on middleware structure and registration.