Flask Context Management: Request Context and Application Context

This article explains the core concept of context in Flask. Context refers to the state and data collection of the current environment, and is divided into two mechanisms: request context and application context. The request context is an exclusive environment for a single request, existing from the request to the response. Its core variables include `request` (which contains request information such as URL and parameters) and `g` (used to share temporary data between different functions within a single request). The lifecycle of the request context is created and destroyed with the request, and different requests do not interfere with each other. The application context is a global environment for the entire application, persisting from application startup to shutdown. The core variable `current_app` is used to access application configurations, instances, etc. All requests share this context, and its lifecycle follows the application's startup and shutdown. The two have significant differences: the request context has a data scope limited to a single request, with `request` and `g` as the core; the application context is global, with `current_app` as the core. It should be noted that `request` should not be used outside of request contexts, `current_app` must be used within an application context, and `g` serves as temporary storage at the request level. Understanding context helps in efficiently managing data transfer and sharing, which is a key foundation for Flask development.