import urllib2
 
request = urllib2.Request('http://example.com/')
request.add_header('User-Agent', 'fake-client')
response = urllib2.urlopen(request)
print request.read()

import urllib,urllib2
 
url = 'http://example.com/'
headers = { 'Host':'example.com',
          'Connection':'keep-alive',
          'Cache-Control':'max-age=0',
          'Accept': 'text/html, */*; q=0.01',
          'X-Requested-With': 'XMLHttpRequest',
          'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.89 Safari/537.36',
          'DNT':'1',
          'Referer': 'http://example.com/',
          'Accept-Encoding': 'gzip, deflate, sdch',
          'Accept-Language': 'zh-CN,zh;q=0.8,ja;q=0.6'
}
data = None
req = urllib2.Request(url, data, headers)
response = urllib2.urlopen(req)
html = response.read()