Python中的urllib

urllib提供了一系列URL的功能。

Get

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

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

from urllib import request

with 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.getheader():
        print('%s: %s' % (k, v))
    print('Data:', data.decode('utf-8'))

可以看到HTTP响应的头和JSON数据：

Stutas：200 OK
Server: nginx
Date: Tue, 26 May 2015 10:02:27 GMT
Content-Type:application/json, charset=utf-8
Content-Length: 2049
Connection: close
Expires: Sun, 1 Jan 2006 01:00:00 GMT
Pragma: no-cache
Cache-Contorl: must-revalidate, no-cache, private
X-DAE-Node: pidll
Data:{"rating": {"max": 10, "numRaters": 16,"average":"7.4","min":0}, "subititle":"","author":["编著"]}，“pubdate”：“2007-6，...”

如果我们想要模仿浏览器发送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iPone 6 去请求豆瓣首页：

from urllib import request

req = request.Request("http://www.douban.com/")
req.add_header('User-Agent', 'Moailla/6.0 (iPone 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'))

这样豆瓣返回适合iPone的移动网页：

...
<meta name = 'viewport' content='width=device-width, user-scalable=no, initial-scale-1.0, minimum-scale=1.0, maxmum-scale=1.0'>
<meta name="format-detection" content=no>
<link rel="apple-touch-icon" sizes="57*57" 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陆，先读取登陆的邮箱和口令，然后按照weibo.cn的登陆页的格式以username=xxx&password=xxx的编码传入：

from urllib import request, parse

print('Login to webo.cn...')
email = input('Email:')
passwd  = input("Passwod:")
login_data = parse.urlencode([
     ('username',email),
     ('password', passwd),
     ('entry', 'mweibo'),
     ('client_id', ''),
     ('savestate', ''),
     ('ec', ''),
     ('pagerefer', 'https://passport.weibo.cn/sigin/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'))

如果登陆成功，我们获得的响应如下：

Status: 200 OK
Server: nginx/1.2.0
...
set-Cookie: SSOLoginState= 1432620126; path=/;domain = weibo.cn
...
Data:{"retcode": 20000000, 'msg':'data':{...,"uid":""}}

如果登陆失败，我们获得的响应如下;

...
Data: {"retcode": 50011015,"msg":"\u7528\u6237\u540d\u6216\u5bc6\u7801\u9519\u8bef","data":{"username":"example@python.org","errine": 536}}

小结

urllib提供的功能就是利用程序去执行各种HTTP请求。吐过要模拟浏览器完成特定功能，需要吧请求伪装成浏览器。伪装的方法是先监控浏览器发出的请求，在根据浏览器的请求头来伪装，User-Agent 头就是用来via哦是浏览器的。