urllib
最后更新于：2022-04-01 01:15:08
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 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":"example@python.org","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。
### 练习
利用urllib读取XML，将XML一节的数据由硬编码改为由urllib获取：
~~~
from urllib import request, parse
def fetch_xml(url):
# 测试
print(fetch_xml('http://weather.yahooapis.com/forecastrss?u=c&w=2151330'))
~~~
Run
### 参考源码
[use_urllib.py](https://github.com/michaelliao/learn-python3/blob/master/samples/commonlib/use_urllib.py)