urllib

    urllib的模块可以非常方便地抓取URL内容，也就是发送一个GET请求到指定的页面，然后返回HTTP的响应：

    例如，对豆瓣的一个URLhttps://api.douban.com/v2/book/2129650进行抓取，并返回响应：

    可以看到HTTP响应的头和JSON数据：

    1. Status: 200 OK
    2. Server: nginx
    3. Date: Tue, 26 May 2015 10:02:27 GMT
    4. Content-Type: application/json; charset=utf-8
    5. Content-Length: 2049
    6. Connection: close
    7. Expires: Sun, 1 Jan 2006 01:00:00 GMT
    8. Pragma: no-cache
    9. Cache-Control: must-revalidate, no-cache, private
    10. X-DAE-Node: pidl1
    11. Data: {"rating":{"max":10,"numRaters":16,"average":"7.4","min":0},"subtitle":"","author":["廖雪峰编著"],"pubdate":"2007-6","tags":[{"count":20,"name":"spring","title":"spring"}...}

    如果我们要想模拟浏览器发送GET请求，就需要使用Request对象，通过往Request对象添加HTTP头，我们就可以把请求伪装成浏览器。例如，模拟iPhone 6去请求豆瓣首页：

    1. from urllib import request
    3. req = request.Request('http://www.douban.com/')
    4. req.add_header('User-Agent', 'Mozilla/6.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/8.0 Mobile/10A5376e Safari/8536.25')
    5. with request.urlopen(req) as f:
    6.     print('Status:', f.status, f.reason)
    7.         print('%s: %s' % (k, v))
    8.     print('Data:', f.read().decode('utf-8'))

    Post

    如果要以POST发送一个请求，只需要把参数以bytes形式传入。

    我们模拟一个微博登录，先读取登录的邮箱和口令，然后按照weibo.cn的登录页的格式以username=xxx&password=xxx的编码传入：

    1. from urllib import request, parse
    3. print('Login to weibo.cn...')
    4. email = input('Email: ')
    5. passwd = input('Password: ')
    6. login_data = parse.urlencode([
    7.     ('username', email),
    8.     ('password', passwd),
    9.     ('entry', 'mweibo'),
    10.     ('client_id', ''),
    11.     ('savestate', '1'),
    12.     ('ec', ''),
    13.     ('pagerefer', 'https://passport.weibo.cn/signin/welcome?entry=mweibo&r=http%3A%2F%2Fm.weibo.cn%2F')
    14. ])
    16. req = request.Request('https://passport.weibo.cn/sso/login')
    17. req.add_header('Origin', 'https://passport.weibo.cn')
    18. req.add_header('User-Agent', 'Mozilla/6.0 (iPhone; CPU iPhone OS 8_0 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/8.0 Mobile/10A5376e Safari/8536.25')
    19. req.add_header('Referer', 'https://passport.weibo.cn/signin/login?entry=mweibo&res=wel&wm=3349&r=http%3A%2F%2Fm.weibo.cn%2F')
    21. with request.urlopen(req, data=login_data.encode('utf-8')) as f:
    23.         print('%s: %s' % (k, v))
    24.     print('Data:', f.read().decode('utf-8'))

    如果登录成功，我们获得的响应如下：

    1. Status: 200 OK
    2. Server: nginx/1.2.0
    3. ...
    4. Set-Cookie: SSOLoginState=1432620126; path=/; domain=weibo.cn
    5. ...
    6. Data: {"retcode":20000000,"msg":"","data":{...,"uid":"1658384301"}}

    如果登录失败，我们获得的响应如下：

    1. proxy_handler = urllib.request.ProxyHandler({'http': 'http://www.example.com:3128/'})
    2. proxy_auth_handler = urllib.request.ProxyBasicAuthHandler()
    3. proxy_auth_handler.add_password('realm', 'host', 'username', 'password')
    4. opener = urllib.request.build_opener(proxy_handler, proxy_auth_handler)
    5. with opener.open('http://www.example.com/login.html') as f:
    6.     pass

    小结

    urllib提供的功能就是利用程序去执行各种HTTP请求。如果要模拟浏览器完成特定功能，需要把请求伪装成浏览器。伪装的方法是先监控浏览器发出的请求，再根据浏览器的请求头来伪装，User-Agent头就是用来标识浏览器的。

    利用urllib读取XML，将XML一节的数据由硬编码改为由urllib获取：

    1. from urllib import request, parse
    3. def fetch_xml(url):
    5.     pass
    7. # 测试

    参考源码

    use_urllib.py