python urllib

urllib — URL handling modules

urllib is a package that collects several modules for working with URLs:

(1) urllib.request for opening and reading URLs
(2) urllib.error containing the exceptions raised by urllib.request
(3) urllib.parse for parsing URLs
(4) urllib.robotparser for parsing robots.txt files

urllib.request.urlopen

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

-         url:  需要打开的网址

-         data：Post提交的数据

-         timeout：设置网站的访问超时时间

直接用urllib.request模块的urlopen（）获取页面，page的数据格式为bytes类型，需要decode（）解码，转换成str类型。

urlopen返回对象提供方法：

-         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网址未找到

-         geturl()：返回请求的url

urllib.request.Request

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

使用request（）来包装请求，再通过urlopen（）获取页面

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')

用来包装头部的数据：

-         User-Agent ：这个头部可以携带如下几条信息：浏览器名和版本号、操作系统名和版本号、默认语言

-         Referer：可以用来防止盗链，有一些网站图片显示来源http://***.com，就是检查Referer来鉴定的

-         Connection：表示连接状态，记录Session的状态

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

urlopen（）的data参数默认为None，当data参数不为空的时候，urlopen（）提交方式为Post

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')
req = request.Request(url, headers=headers, data=data)
page = request.urlopen(req).read()
page = page.decode('utf-8')

 urllib.parse.urlencode

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

urlencode（）主要作用就是将url附上要提交的数据

data = {
    'first': 'true',
    'pn': 1,
    'kd': 'Python'
}
data = parse.urlencode(data).encode('utf-8')

urllib.urlretrieve

urlretrieve(url, filename=None, reporthook=None, data=None):

    """
    Retrieve a URL into a temporary location on disk.

    Requires a URL argument. If a filename is passed, it is used as
    the temporary file location. The reporthook argument should be
    a callable that accepts a block number, a read size, and the
    total file size of the URL target. The data argument should be
    valid URL encoded data.

    If a filename is passed and the URL points to a local resource,
    the result is a copy from local file to new file.

    Returns a tuple containing the path to the newly created
    data file as well as the resulting HTTPMessage object.
    """