3. urllib
    5. 阅读: 201907
    6. urllib提供了一系列用于操作URL的功能。
    8. Get
    10. 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：
    12. 例如，对豆瓣的一个URLhttps://api.douban.com/v2/book/2129650进行抓取，并返回响应：
    14. from urllib import request
    16. with request.urlopen('https://api.douban.com/v2/book/2129650') as f:
    17.    data = f.read()
    18.    print('Status:', f.status, f.reason)
    19.    for k, v in f.getheaders():
    20.        print('%s: %s' % (k, v))
    21.    print('Data:', data.decode('utf-8'))
    22. 可以看到HTTP响应的头和JSON数据：
    24. Status: 200 OK
    25. Server: nginx
    26. Date: Tue, 26 May 2015 10:02:27 GMT
    27. Content-Type: application/json; charset=utf-8
    28. Content-Length: 2049
    29. Connection: close
    30. Expires: Sun, 1 Jan 2006 01:00:00 GMT
    31. Pragma: no-cache
    32. Cache-Control: must-revalidate, no-cache, private
    33. X-DAE-Node: pidl1
    34. Data: {"rating":{"max":10,"numRaters":16,"average":"7.4","min":0},"subtitle":"","author":["廖雪峰编著"],"pubdate":"2007-6",...}
    35. 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：
    37. from urllib import request
    39. req = request.Request('http://www.douban.com/')
    40. 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')
    41. with request.urlopen(req) as f:
    42.    print('Status:', f.status, f.reason)
    43.    for k, v in f.getheaders():
    44.        print('%s: %s' % (k, v))
    45.    print('Data:', f.read().decode('utf-8'))
    46. 这样豆瓣会返回适合iPhone的移动版网页：
    48. ...
    49.    <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0">
    50.    <meta name="format-detection" content="telephone=no">
    51.    <link rel="apple-touch-icon" sizes="57x57" href="http://img4.douban.com/pics/cardkit/launcher/57.png" />
    52. ...
    53. Post
    55. 如果要以POST发送一个请求，只需要把参数data以bytes形式传入。
    57. 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：
    59. from urllib import request, parse
    61. print('Login to weibo.cn...')
    62. email = input('Email: ')
    63. passwd = input('Password: ')
    64. login_data = parse.urlencode([
    65.    ('username', email),
    66.    ('password', passwd),
    67.    ('entry', 'mweibo'),
    68.    ('client_id', ''),
    69.    ('savestate', '1'),
    70.    ('ec', ''),
    71.    ('pagerefer', 'https://passport.weibo.cn/signin/welcome?entry=mweibo&r=http%3A%2F%2Fm.weibo.cn%2F')
    72. ])
    74. req = request.Request('https://passport.weibo.cn/sso/login')
    75. req.add_header('Origin', 'https://passport.weibo.cn')
    76. 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')
    77. req.add_header('Referer', 'https://passport.weibo.cn/signin/login?entry=mweibo&res=wel&wm=3349&r=http%3A%2F%2Fm.weibo.cn%2F')
    79. with request.urlopen(req, data=login_data.encode('utf-8')) as f:
    80.    print('Status:', f.status, f.reason)
    81.    for k, v in f.getheaders():
    82.        print('%s: %s' % (k, v))
    83.    print('Data:', f.read().decode('utf-8'))
    84. 如果登录成功，我们获得的响应如下：
    86. Status: 200 OK
    87. Server: nginx/1.2.0
    88. ...
    89. Set-Cookie: SSOLoginState=1432620126; path=/; domain=weibo.cn
    90. ...
    91. Data: {"retcode":20000000,"msg":"","data":{...,"uid":"1658384301"}}
    92. 如果登录失败，我们获得的响应如下：
    94. ...
    95. Data: {"retcode":50011015,"msg":"\u7528\u6237\u540d\u6216\u5bc6\u7801\u9519\u8bef","data":{"username":"example@python.org","errline":536}}
    96. Handler
    98. 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：
    100. proxy_handler = urllib.request.ProxyHandler({'http': 'http://www.example.com:3128/'})
    101. proxy_auth_handler = urllib.request.ProxyBasicAuthHandler()
    102. proxy_auth_handler.add_password('realm', 'host', 'username', 'password')
    103. opener = urllib.request.build_opener(proxy_handler, proxy_auth_handler)
    104. with opener.open('http://www.example.com/login.html') as f:
    105.    pass
    106. 小结
    108. 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。
    110. 练习
    112. 利用urllib读取JSON，然后将JSON解析为Python对象：
    114. # -*- coding: utf-8 -*-
    115. from urllib import request
    117. def fetch_data(url):
    118.    return ''
    120. # 测试
    121. URL = 'https://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20weather.forecast%20where%20woeid%20%3D%202151330&format=json'
    122. data = fetch_data(URL)
    123. print(data)
    124. assert data['query']['results']['channel']['location']['city'] == 'Beijing'
    125. print('ok')
    126. Run
    127. 参考源码
    129. use_urllib.py