之前以为urllib2只能发送GET和POST请求，原来是可用修改的：

# urlib2发送HEAD请求
import urllib2
request = urllib2.Request('http://www.redicecn.com')
request.get_method = lambda : 'HEAD'
response = urllib2.urlopen(request)
print dict(response.info())

{'content-length': '25857', 'accept-ranges': 'bytes', 'server': 'Apache/2.2.21 (EL)', 'last-modified': 'Wed, 04 Jan 2012 07:37:36 GMT', 'connection': 'close', 'etag': '"13a5bc-6501-4b5aee3b3f000"', 'date': 'Wed, 04 Jan 2012 07:53:50 GMT', 'content-type': 'text/html'}