Exception handling in routes in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of exception handling in Flask routes?

Exception handling in Flask routes helps catch errors during request processing to prevent the app from crashing and to provide meaningful error messages to users.

beginner

How do you catch exceptions inside a Flask route function?

You use a try-except block inside the route function to catch exceptions and handle them gracefully.

intermediate

What Flask decorator can be used to handle exceptions globally for all routes?

The @app.errorhandler decorator is used to define a function that handles specific exceptions or HTTP error codes globally.

intermediate

What is the benefit of using @app.errorhandler over try-except in each route?

Using @app.errorhandler centralizes error handling, reduces repeated code, and ensures consistent error responses across all routes.

beginner

How can you return a custom error message and status code when an exception occurs in a Flask route?

Inside the except block or error handler, return a Flask response with a message and a status code, e.g., return {'error': 'Not found'}, 404.

Which Flask decorator is used to handle exceptions globally?

A @app.errorhandler

B @app.route

C @app.catch

D @app.exception

The @app.errorhandler decorator is designed to catch exceptions or HTTP errors globally in Flask.

What happens if an exception is not caught in a Flask route?

A Flask returns a default 500 Internal Server Error response

B The app crashes immediately

C The request is retried automatically

D Nothing, the exception is ignored

If an exception is uncaught, Flask returns a 500 Internal Server Error response by default.

Where should you place try-except blocks for best practice in Flask apps?

A Only in the main app file

B Preferably in global error handlers using @app.errorhandler

C Inside each route function

D In the HTML templates

Global error handlers with @app.errorhandler centralize error handling and keep code clean.

How do you return a 404 error with a custom message in a Flask route?

A raise Exception('Not found')

B abort(200)

C return 'Not found'

D return {'error': 'Not found'}, 404

Returning a tuple with a dictionary and status code sends a custom JSON message with the 404 status.

What is commonly used to abort a request with an HTTP error in Flask?

A ValueError

B KeyError

C flask.abort

D flask.RequestException

The flask.abort function raises an HTTPException to abort a request with a specific HTTP status code.

Explain how to handle exceptions inside a Flask route and how to provide a custom error response.

Think about using try-except and returning a tuple with message and code.

Describe the use and benefits of the @app.errorhandler decorator in Flask.

Consider how centralizing error handling helps maintain your app.