Python3之urllib模块

简介

　　urllib是python的一个获取url(Uniform Resource Locators，统一资源定位符)，可以用来抓取远程的数据。

常用方法

（1）urlopen

　　urllib.request.urlopen(url, data=None,[timeout,]*,cafile=None,capath=None,cadefault=False,context=None)

urllib.request.urlopen() 可以获取页面，获取页面内容的数据格式为bytes类型，需要进行decode()解码，转换成str类型。

参数说明：

• url : 需要打开的网址
• data : 字典形式，默认为None时是GET方法，data不为空时, urlopen()的提交方式为POST，注意POST提交时，data需要转换为字节;
• timeout : 设置网站访问的超时时间

from urllib import request
response =  request.urlopen("http://members.3322.org/dyndns/getip")
# <http.client.HTTPResponse object at 0x031F63B0>
page = response.read()
# b'106.37.169.186\n'
page = page.decode("utf-8")
# '106.37.169.186\n'

# 使用with语句
with request.urlopen("http://members.3322.org/dyndns/getip") as response:
    page = response.read()
    print(page.decode("utf-8"))

　　注意：urllib.request 使用相同的接口来处理所有类型的url，比如：

req = urllib.request.urlopen('ftp://example.com/')

　　

　　urlopen返回对象提供的方法：

• read(),readline(),readlines(),fileno(),close() : 对HTTPResponse类型数据进行操作
• info() : 返回HTTPMessage对象，表示远程服务器返回的头信息
• getcode() : 返回HTTP状态码，如果是http请求，200请求成功完成，404网页未找到
• geturl(): 返回请求的url

（2）Request

　　urllib.request.Request(url,data=None,headers={},method=None)

from urllib import request

url = r'http://www.lagou.com/zhaopin/Python/?labelWords=label'
headers = {
    'User-Agent': r'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) '
                  r'Chrome/45.0.2454.85 Safari/537.36 115Browser/6.0.3',
    'Referer': r'http://www.lagou.com/zhaopin/Python/?labelWords=label',
    'Connection': 'keep-alive'
}
req = request.Request(url, headers=headers)
page = request.urlopen(req).read()
page = page.decode('utf-8')

　　

（3）parse.urlencode

　　urllib.parse.urlencode(query, doseq=False,safe='',encoding=None,errors=None)

urlencode()的主要作用就是将url附上要提交的数据. 对data数据进行编码。

from urllib import request, parse
url = r'http://www.lagou.com/jobs/positionAjax.json?'
headers = {
    'User-Agent': r'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) '
                  r'Chrome/45.0.2454.85 Safari/537.36 115Browser/6.0.3',
    'Referer': r'http://www.lagou.com/zhaopin/Python/?labelWords=label',
    'Connection': 'keep-alive'
}
data = {
    'first': 'true',
    'pn': 1,
    'kd': 'Python'
}
data = parse.urlencode(data).encode('utf-8')
# 此时data是字节 b'first=true&pn=1&kd=Python' ，POST的数据必须是bytes或者iterable of bytes，不能是str，因此需要encode编码
# 经过urlencode转换后的data数据为'first=true&pn=1&kd=Python'
# 最后提交的url为：http://www.lagou.com/jobs/positionAjax.json?first=true?pn=1?kd=Python
req = request.Request(url, headers=headers, data=data)
# 此时req : <urllib.request.Request object at 0x02F52A30>
page = request.urlopen(req).read()
# 此时page是字节： b'{"success":false,"msg":"\xe6\x82\xa8\xe6\x93\x8d\xe4\xbd\x9c\xe5\xa4\xaa\xe9\xa2\x91\xe7\xb9\x81,\xe8\xaf\xb7\xe7\xa8\x8d\xe5\x90\x8e\xe5\x86\x8d\xe8\xae\xbf\xe9\x97\xae","clientIp":"106.37.169.186"}\n
page = page.decode('utf-8')
# 此时page是字符串："success":false,"msg":"您操作太频繁,请稍后再访问","clientIp":"106.37.169.186"}

　　

（4）代理 request.ProxyHandler(proxies=None)

当需要抓取的网站设置了访问限制，这时就需要用到代理来抓取数据。

from urllib import request, parse
data = {
        'first': 'true',
        'pn': 1,
        'kd': 'Python'
    }
proxy = request.ProxyHandler({'http': '5.22.195.215:80'})  # 设置proxy
opener = request.build_opener(proxy)  # 挂载opener
request.install_opener(opener)  # 安装opener
data = parse.urlencode(data).encode('utf-8')
page = opener.open(url, data).read()
page = page.decode('utf-8')
return page

　　

（5）异常处理

　　urlopen在不能处理某个响应的时候会抛出URLError， HTTPError是URLError的子类，在遇到HTTP URL的特殊情况时被抛出。异常类来自于 urllib.error 模块。

URLError :

　　一般来说，URLError被抛出是因为没有网络连接(没有到指定服务器的路径)，或者是指定服务器不存在。在这种情况下，抛出的异常将会包含一个‘reason’属性，
这是包含一个错误码和一段错误信息的元组.

req = urllib.request.Request('http://www.pretend_server.org')
try:
	urllib.request.urlopen(req)
except urllib.error.URLError as e:
    print(e.reason)
# 输出
(4, 'getaddrinfo failed')

　　

HTTPError :
　　每一个来自服务器的HTTP响应都包含一个数字的“状态码”。有时状态码表明服务器不能执行请求。默认的处理程序会为你处理其中的部分响应(比如，如果响应是“重定向”，
要求客户端从一个不同的URL中获取资料，那么urllib将会为你处理这个)。对于那些不能处理的响应，urlopen将会抛出一个HTTPError。
典型的错误包括‘404’(页面未找到)，‘403’(请求禁止)，和‘401’(请求认证)。

# Table mapping response codes to messages; entries have the
# form {code: (shortmessage, longmessage)}.
responses = {
    100: ('Continue', 'Request received, please continue'),
    101: ('Switching Protocols',
          'Switching to new protocol; obey Upgrade header'),

    200: ('OK', 'Request fulfilled, document follows'),
    201: ('Created', 'Document created, URL follows'),
    202: ('Accepted',
          'Request accepted, processing continues off-line'),
    203: ('Non-Authoritative Information', 'Request fulfilled from cache'),
    204: ('No Content', 'Request fulfilled, nothing follows'),
    205: ('Reset Content', 'Clear input form for further input.'),
    206: ('Partial Content', 'Partial content follows.'),

    300: ('Multiple Choices',
          'Object has several resources -- see URI list'),
    301: ('Moved Permanently', 'Object moved permanently -- see URI list'),
    302: ('Found', 'Object moved temporarily -- see URI list'),
    303: ('See Other', 'Object moved -- see Method and URL list'),
    304: ('Not Modified',
          'Document has not changed since given time'),
    305: ('Use Proxy',
          'You must use proxy specified in Location to access this '
          'resource.'),
    307: ('Temporary Redirect',
          'Object moved temporarily -- see URI list'),

    400: ('Bad Request',
          'Bad request syntax or unsupported method'),
    401: ('Unauthorized',
          'No permission -- see authorization schemes'),
    402: ('Payment Required',
          'No payment -- see charging schemes'),
    403: ('Forbidden',
          'Request forbidden -- authorization will not help'),
    404: ('Not Found', 'Nothing matches the given URI'),
    405: ('Method Not Allowed',
          'Specified method is invalid for this server.'),
    406: ('Not Acceptable', 'URI not available in preferred format.'),
    407: ('Proxy Authentication Required', 'You must authenticate with '
          'this proxy before proceeding.'),
    408: ('Request Timeout', 'Request timed out; try again later.'),
    409: ('Conflict', 'Request conflict.'),
    410: ('Gone',
          'URI no longer exists and has been permanently removed.'),
    411: ('Length Required', 'Client must specify Content-Length.'),
    412: ('Precondition Failed', 'Precondition in headers is false.'),
    413: ('Request Entity Too Large', 'Entity is too large.'),
    414: ('Request-URI Too Long', 'URI is too long.'),
    415: ('Unsupported Media Type', 'Entity body in unsupported format.'),
    416: ('Requested Range Not Satisfiable',
          'Cannot satisfy request range.'),
    417: ('Expectation Failed',
          'Expect condition could not be satisfied.'),

    500: ('Internal Server Error', 'Server got itself in trouble'),
    501: ('Not Implemented',
          'Server does not support this operation'),
    502: ('Bad Gateway', 'Invalid responses from another server/proxy.'),
    503: ('Service Unavailable',
          'The server cannot process the request due to a high load'),
    504: ('Gateway Timeout',
          'The gateway server did not receive a timely response'),
    505: ('HTTP Version Not Supported', 'Cannot fulfill request.'),
    }

错误码

　　

　　异常处理方式：

req = urllib.request.Request('http://www.python.org/fish.html')
try:
    urllib.request.urlopen(req)
except urllib.error.HTTPError as e:
    print (e.code)
    print (e.info())
    print (e.geturl())
    print (e.read())

　　或者：

from urllib.request import Request, urlopen
from urllib.error import URLError
req = Request(someurl)
try:
    response = urlopen(req)
except URLError as e:
    if hasattr(e, 'reason'):
        print('We failed to reach a server.')
        print('Reason: ', e.reason)
    elif hasattr(e, 'code'):
        print('The server couldn\'t fulfill the request.')
        print('Error code: ', e.code)