python3中也有urllib和urllib3两个库，其中urllib几乎是python2.7中urllib和urllib2两个模块的集合，所以我们最常用的urllib模块，而urllib3则作为一个拓展模块使用。
python2.7中的urllib2 = python3中的urllib.request
通常python2.7中的urllib2在移植到python3中时可以改写成import urllib.request as urllib2
举例:
Python2:
>>> import urllib2
>>> response=urllib2.urlopen('http://www.baidu.com/')
>>> print(response.read())
Python3:
>>> import urllib.request
>>> response=urllib.request.urlopen('http://www.baidu.com/')
>>> print(response.read())
可以使用dir(urllib)和dir(urllib2)在python2.7和python3环境中分别打印库中的所有函数
Python 2 name
urllib.urlretrieve()
urllib.urlcleanup()
urllib.quote()
urllib.quote_plus()
urllib.unquote()
urllib.unquote_plus()
urllib.urlencode()
urllib.pathname2url()
urllib.url2pathname()
urllib.getproxies()
urllib.URLopener
urllib.FancyURLopener
urllib.ContentTooShortError
urllib2.urlopen()
urllib2.install_opener()
urllib2.build_opener()
urllib2.URLError
urllib2.HTTPError
urllib2.Request
urllib2.OpenerDirector
urllib2.BaseHandler
urllib2.HTTPDefaultErrorHandler
urllib2.HTTPRedirectHandler
urllib2.HTTPCookieProcessor
urllib2.ProxyHandler
urllib2.HTTPPasswordMgr
urllib2.HTTPPasswordMgrWithDefaultRealm
urllib2.AbstractBasicAuthHandler
urllib2.HTTPBasicAuthHandler
urllib2.ProxyBasicAuthHandler
urllib2.AbstractDigestAuthHandler
urllib2.HTTPDigestAuthHandler
urllib2.ProxyDigestAuthHandler
urllib2.HTTPHandler
urllib2.HTTPSHandler
urllib2.FileHandler
urllib2.FTPHandler
urllib2.CacheFTPHandler
urllib2.UnknownHandler
Python 3 name
urllib.request.urlretrieve()
urllib.request.urlcleanup()
urllib.parse.quote()
urllib.parse.quote_plus()
urllib.parse.unquote()
urllib.parse.unquote_plus()
urllib.parse.urlencode()
urllib.request.pathname2url()
urllib.request.url2pathname()
urllib.request.getproxies()
urllib.request.URLopener
urllib.request.FancyURLopener
urllib.error.ContentTooShortError
urllib.request.urlopen()
urllib.request.install_opener()
urllib.request.build_opener()
urllib.error.URLError
urllib.error.HTTPError
urllib.request.Request
urllib.request.OpenerDirector
urllib.request.BaseHandler
urllib.request.HTTPDefaultErrorHandler
urllib.request.HTTPRedirectHandler
urllib.request.HTTPCookieProcessor
urllib.request.ProxyHandler
urllib.request.HTTPPasswordMgr
urllib.request.HTTPPasswordMgrWithDefaultRealm
urllib.request.AbstractBasicAuthHandler
urllib.request.HTTPBasicAuthHandler
urllib.request.ProxyBasicAuthHandler
urllib.request.AbstractDigestAuthHandler
urllib.request.HTTPDigestAuthHandler
urllib.request.ProxyDigestAuthHandler
urllib.request.HTTPHandler
urllib.request.HTTPSHandler
urllib.request.FileHandler
urllib.request.FTPHandler
urllib.request.CacheFTPHandler
urllib.request.UnknownHandler