urllib · 廖雪峰的Python3.x教程

### 介绍 `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":"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): pass # 测试 print(fetch_xml('http://weather.yahooapis.com/forecastrss?u=c&w=2151330')) ~~~