1.HTTP通信简介
计算机发出请求会遵照下面的格式：
GET /index.html HTTP/1.1
Host: www.example.com通过一次HTTP交易，客户端从服务器那里获得了自己请求的资源，即这里的文本。上面是对HTTP协议工作过程的一个简要介绍，省略了很多细节。
2. http.client 包
HTTP请求最重要的一些信息是主机地址、请求方法和资源路径。只要明确这些信息，再加上Python标准库中的http.client包的帮助，就可以发出HTTP请求了。
import http.client
conn = http.client.HTTPConnection("www.example.com") #主机地址
conn.request("GET","/") #请求方法和资源路径
response = conn.getresponse() #获得回复
print(response.status,response.reason) #回复的状态码和状态描述
content = response.read() #回复的主体内容
print(content)
——————————————————
200 OK
b'<!doctype html>\n<html>\n<head>\n <title>Example Domain</title>\n\n <meta charset="utf-8" />\n <meta http-equiv="Content-type" content="text/html; charset=utf-8" />\n <meta name="viewport" content="width=device-width, initial-scale=1" />\n <style type="text/css">\n body {\n background-color: #f0f0f2;\n margin: 0;\n padding: 0;\n font-family: -apple-system, system-ui, BlinkMacSystemFont, "Segoe UI", "Open Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;\n \n }\n div {\n width: 600px;\n margin: 5em auto;\n padding: 2em;\n background-color: #fdfdff;\n border-radius: 0.5em;\n box-shadow: 2px 3px 7px 2px rgba(0,0,0,0.02);\n }\n a:link, a:visited {\n color: #38488f;\n text-decoration: none;\n }\n @media (max-width: 700px) {\n div {\n margin: 0 auto;\n width: auto;\n }\n }\n </style> \n</head>\n\n<body>\n<div>\n <h1>Example Domain</h1>\n <p>This domain is for use in illustrative examples in documents. You may use this\n domain in literature without prior coordination or asking for permission.</p>\n <p><a href="https://www.iana.org/domains/example">More information...</a></p>\n</div>\n</body>\n</html>\n'
