link: http://blog.sina.com.cn/s/blog_76a0e17a0100q762.html

select — Waiting for I/O completion

This module provides access to the select() and poll() functions available in most operating systems. Note that on? Windows , it only works for sockets; on other operating systems, it also works for other file types (in particular, on Unix, it works on pipes). It cannot be u sed ? on regular files to determine whether a file has grown since it was last read.
这个模块提供的 select() 和 poll() 方法可用于大部分 操作系统 。注意：在?