import urllib.request, urllib.error, urllib.parse

BROWSER = 'Mozilla/5.0 (Windows NT 5.1; rv:20.0) Gecko/20100101 Firefox/20.0'
URL = 'http://www.python.org'

def spoof_firefox():

    opener = urllib.request.build_opener()
    opener.addheaders = [('User-agent', BROWSER)]
    result = opener.open(URL)
    print ("Response headers:")

    for header in  result.headers:
        print ("%s: %s" %(header, result.headers.get(header)))
        
if __name__ == '__main__':
    spoof_firefox()