# urllib urllib提供了一系列用于操作URL的功能。 ## Get urllib的`request`模塊可以非常方便地抓取URL內容，也就是發送一個GET請求到指定的頁面，然后返回HTTP的響應： 例如，對豆瓣的一個URL`https://api.douban.com/v2/book/2129650`進行抓取，并返回響應： ``` 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響應的頭和JSON數據： ``` 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":["廖雪峰編著"],"pubdate":"2007-6","tags":[{"count":20,"name":"spring","title":"spring"}...} ``` 如果我們要想模擬瀏覽器發送GET請求，就需要使用`Request`對象，通過往`Request`對象添加HTTP頭，我們就可以把請求偽裝成瀏覽器。例如，模擬iPhone 6去請求豆瓣首頁： ``` 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')) ``` 這樣豆瓣會返回適合iPhone的移動版網頁： ``` ... <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發送一個請求，只需要把參數`data`以bytes形式傳入。 我們模擬一個微博登錄，先讀取登錄的郵箱和口令，然后按照weibo.cn的登錄頁的格式以`username=xxx&password=xxx`的編碼傳入： ``` 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')) ``` 如果登錄成功，我們獲得的響應如下： ``` Status: 200 OK Server: nginx/1.2.0 ... Set-Cookie: SSOLoginState=1432620126; path=/; domain=weibo.cn ... Data: {"retcode":20000000,"msg":"","data":{...,"uid":"1658384301"}} ``` 如果登錄失敗，我們獲得的響應如下： ``` ... Data: {"retcode":50011015,"msg":"\u7528\u6237\u540d\u6216\u5bc6\u7801\u9519\u8bef","data":{"username":"example@python.org","errline":536}} ``` ## Handler 如果還需要更復雜的控制，比如通過一個Proxy去訪問網站，我們需要利用`ProxyHandler`來處理，示例代碼如下： ``` 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 ``` ## 小結 urllib提供的功能就是利用程序去執行各種HTTP請求。如果要模擬瀏覽器完成特定功能，需要把請求偽裝成瀏覽器。偽裝的方法是先監控瀏覽器發出的請求，再根據瀏覽器的請求頭來偽裝，`User-Agent`頭就是用來標識瀏覽器的。 ## 練習 利用urllib讀取XML，將XML一節的數據由硬編碼改為由urllib獲取： ``` from urllib import request, parse def fetch_xml(url): pass # 測試 print(fetch_xml('http://weather.yahooapis.com/forecastrss?u=c&w=2151330')) ``` ## 參考源碼 [use_urllib.py](https://github.com/michaelliao/learn-python3/blob/master/samples/commonlib/use_urllib.py)