python3:urllib.request 的主要函数说明

内容的主要来源为：

https://docs.python.org/3/library/urllib.request.html#module-urllib.request

The urllib.request module defines functions and classes which help in opening URLs (mostly HTTP) in a complex world — basic and digest authentication, redirections, cookies and more.

urllib.request.urlopen(url, data=None, [timeout, ]*, cafile=None, capath=None, cadefault=False, context=None)

url, which can be either a string or a Request object.
     url 既可以是一个string, 也可以是一个request对象
data must be an object specifying additional data to be sent to the server, or None if no such data is needed. See Request for details
     data 必须是指定发送给sever的特定附加数据, 当这个数据不需要，则data=None
函数返回的是什么？
This function always returns an object which can work as a context manager and has methods such as

这个函数总是返回一个可以作为上下文的管理器.并有如下的方法:

实例如下：

from urllib import request

if __name__ == '__main__':
    url = 'http://www.baidu.com/'
    response = request.urlopen(url)
    html = response.read().decode('utf-8')
    print(html)

其它几个函数的实例如下(from ipython)