四十九 經常使用內建模塊 urllib

urllib提供了一系列用於操做URL的功能。

Get

urllib的request模塊能夠很是方便地抓取URL內容，也就是發送一個GET請求到指定的頁面，而後返回HTTP的響應：

例如，對豆瓣的一個URLhttps://api.douban.com/v2/book/2129650進行抓取，並返回響應：

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'))

能夠看到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":["廖雪峯編著"],"pubdate":"2007-6","tags":[{"count":20,"name":"spring","title":"spring"}...}

若是咱們要想模擬瀏覽器發送GET請求，就須要使用Request對象，經過往Request對象添加HTTP頭，咱們就能夠把請求假裝成瀏覽器。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

若是要以POST發送一個請求，只須要把參數data以bytes形式傳入。

咱們模擬一個微博登陸，先讀取登陸的郵箱和口令，而後按照weibo.cn的登陸頁的格式以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'))

若是登陸成功，咱們得到的響應以下：

Status: 200 OK
Server: nginx/1.2.0
...
Set-Cookie: SSOLoginState=1432620126; path=/; domain=weibo.cn
...
Data: {"retcode":20000000,"msg":"","data":{...,"uid":"1658384301"}}

若是登陸失敗，咱們得到的響應以下：

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

Handler

若是還須要更復雜的控制，好比經過一個Proxy去訪問網站，咱們須要利用ProxyHandler來處理，示例代碼以下：

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類HTTP請求。若是要模擬瀏覽器完成特定功能，須要把請求假裝成瀏覽器。假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假裝，User-Agent頭就是用來標識瀏覽器的。