A template is actually a file containing response text, which is used to render response data (views can render data, templates help the view to complete some functions, and the view is only responsible for processing business logic), in which placeholders (variables) are used to represent dynamic parts , which tells the template engine that its concrete value needs to be obtained from the used data. Jinja2 engine
1. Variable {{variable name}}: accept the response data returned by the view function