import urllib 
    import os 
    import shutil 

    hostspath = "C:\\Windows\\System32\\drivers\\etc" 
    savepath = hostspath + "\\hostsave" 

    def download_hosts(url = "http://my-hosts-file.googlecode.com/svn/trunk/hosts"): 
        os.chdir(hostspath) 
        if os.getcwd() != hostspath: 
            print("Switch Dir to System32 Error,check permission!\npwd:"+os.getcwd()) 
            exit()  
        try: 
            urllib.urlretrieve(url, "hostsave") 
        except: 
            print '\t Error when retrieveing hosts file from url: ', url 

    def backup_hosts(): 
        shutil.copy("hosts","hosts.bak") 

    def replace_hosts(): 
        shutil.copy("hostsave", "hosts") 
        print("Replace original hosts file finished, then flush dns...") 
        os.remove(savepath)     
        os.system("ipconfig /flushdns") 

    def main(): 
        download_hosts() 
        backup_hosts() 
        replace_hosts() 
    if __name__ == '__main__': 
        main()