divided into three major components: A web framework (including RequestHandler which is subclassed to create web applications, and various supporting classes). Client- and server-side implementions of HTTP with Tornado 6.2 and Python 3.10, the recommended pattern for starting a Tornado application is to create a main coroutine to be run with asyncio.run [https://docs.python.org/3/library/asyncio-runner.html#asyncio RequestHandler are designed to be overridden by subclasses when necessary. On every request, the following sequence of calls takes place: 1. A new RequestHandler object is created on each request. 2. initialize()

into three major components: • A web framework (including RequestHandler which is subclassed to create web applications, and various supporting classes). • Client- and server-side implementions of HTTP with Tornado 6.2 and Python 3.10, the recommended pattern for starting a Tornado application is to create a main coroutine to be run with asyncio.run. (In older versions, it was common to do initialization RequestHandler are designed to be overridden by sub- classes when necessary. On every request, the following sequence of calls takes place: 1. A new RequestHandler object is created on each request. 2. initialize()

=> file, Err(error) => match error.kind() { ErrorKind::NotFound => match File::create("hello.txt") { Ok(fc) => fc, Err(e) => panic!("Problem creating the match。 我们希望在内层 match 中检查的条件是 error.kind() 的返回值是否为 ErrorKind的 NotFound 变体。如果是，则通过 File::create 尝试创建该文件。然而因为 File::create 也可能会失 败，还需要在内层 match 表达式中增加了第二个分支。当文件不能被创建，会打印出一个不同 的错误信息。外层 match 的最后一个分支保持不变，这样对任何除了文件不存在的错误会使程 txt").unwrap_or_else(|error| { if error.kind() == ErrorKind::NotFound { File::create("hello.txt").unwrap_or_else(|error| { panic!("Problem creating the file: {error: