四十九 常用内建模块 urllib

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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URLhttps://api.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.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 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-Control: must-revalidate, no-cache, private
X-DAE-Node: pidl1
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:

from urllib import request

req = 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, parse

print(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 OK
Server: 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":"[email protected]","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。

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