Error handling and debugging

When something goes wrong in your application, it's important to be able to control what responses will the clients will receive. In HTML web apps, you usually get specific HTML pages when you encounter a 404 or a 50x error, and that's how Flask works out of the box. But when building microservices, you need to have more control on what should be sent back to the client--that's where custom error handlers come in handy.

The other important feature is the ability to debug what's wrong with your code when an unexpected error occurs. And Flask comes with a built-in debugger we'll discover in this section, which can be activated when your app runs in the debug mode.