urllib

urllib提供了一系列用于操作URL的功能。

Get

urllib的request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URL https://api.douban.com/v2/book/2129650进行抓取，并返回响应：

from urllib import requestwith request.urlopen('https://api.douban.com/v2/book/2129650') as f:    data = f.read()    print('Status:', f.status, f.reason)    for k, v in f.getheaders():        print('%s: %s' % (k, v))    print('Data:', data.decode('utf-8'))

可以看到HTTP响应的头和JSON数据：

Status: 200 OKServer: nginxDate: Tue, 26 May 2015 10:02:27 GMTContent-Type: application/json; charset=utf-8Content-Length: 2049Connection: closeExpires: Sun, 1 Jan 2006 01:00:00 GMTPragma: no-cacheCache-Control: must-revalidate, no-cache, privateX-DAE-Node: pidl1Data: {"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：

from urllib import requestreq = request.Request('http://www.douban.com/')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')with request.urlopen(req) as f:    print('Status:', f.status, f.reason)    for k, v in f.getheaders():        print('%s: %s' % (k, v))    print('Data:', f.read().decode('utf-8'))

这样豆瓣会返回适合iPhone的移动版网页：

...    <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0">    <meta name="format-detection" content="telephone=no">    <link rel="apple-touch-icon" sizes="57x57" href="http://img4.douban.com/pics/cardkit/launcher/57.png" />...

Post

如果要以POST发送一个请求，只需要把参数data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：

from urllib import request, parseprint('Login to weibo.cn...')email = input('Email: ')passwd = input('Password: ')login_data = parse.urlencode([    ('username', email),    ('password', passwd),    ('entry', 'mweibo'),    ('client_id', ''),    ('savestate', '1'),    ('ec', ''),    ('pagerefer', 'https://passport.weibo.cn/signin/welcome?entry=mweibo&r=http%3A%2F%2Fm.weibo.cn%2F')])req = request.Request('https://passport.weibo.cn/sso/login')req.add_header('Origin', 'https://passport.weibo.cn')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')req.add_header('Referer', 'https://passport.weibo.cn/signin/login?entry=mweibo&res=wel&wm=3349&r=http%3A%2F%2Fm.weibo.cn%2F')with request.urlopen(req, data=login_data.encode('utf-8')) as f:    print('Status:', f.status, f.reason)    for k, v in f.getheaders():        print('%s: %s' % (k, v))    print('Data:', f.read().decode('utf-8'))

如果登录成功，我们获得的响应如下：

Status: 200 OKServer: nginx/1.2.0...Set-Cookie: SSOLoginState=1432620126; path=/; domain=weibo.cn...Data: {"retcode":20000000,"msg":"","data":{...,"uid":"1658384301"}}

如果登录失败，我们获得的响应如下：

...Data: {"retcode":50011015,"msg":"\u7528\u6237\u540d\u6216\u5bc6\u7801\u9519\u8bef","data":{"username":"[e-mail]","errline":536}}Handler

如果还需要更复杂的控制，比如通过一个Proxy去访问网站，我们需要利用ProxyHandler来处理，示例代码如下：

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