Signals in Flask for Application Lifecycle

# Introduction

In this lab, you will learn how to use signals in Flask, which are a lightweight way to notify subscribers of certain events during the lifecycle of the application and each request. Signals allow you to perform actions in response to specific events without directly affecting the application code. They are useful for testing, metrics, auditing, and more.

> Note: You need to create the code file yourself and run it in the environment. You can preview the Flask service status on Web 5000.