Распараллеливание цикла

#loop around to get every tile
for j in xrange(ht):
    for i in xrange(wt):
        filename = "%04d-%04d.jpg"%(j,i)
        pathfilename = str(photo_id)+"/"+filename
        if not os.path.exists(pathfilename) :
            url = "%s/get_ge_tile/%d/%d/%d/%d"%(base,photo_id, level,j,i)
            progress = (j)*wt+i+1
            print '('+str(progress)+'/'+str(wt*ht)+') Downloading '+str(url)+' as '+str(filename)
            h = urlopen(url)
            if 200 == h.code :
                fout = open(pathfilename,"wb")
                fout.write(h.read())
                fout.close()
            else:
                print '('+str(progress)+'/'+str(wt*ht)+') Downloading error '+str(url)+' http code '+str(h.code)
                ++errors

Traceback (most recent call last):
  File "C:\gigapandown\gigapanDownloader.py", line 95, in <module>
    h = urlopen(url)
  File "C:\Python27\lib\urllib.py", line 87, in urlopen
    return opener.open(url)
  File "C:\Python27\lib\urllib.py", line 213, in open
    return getattr(self, name)(url)
  File "C:\Python27\lib\urllib.py", line 350, in open_http
    h.endheaders(data)
  File "C:\Python27\lib\httplib.py", line 1038, in endheaders
    self._send_output(message_body)
  File "C:\Python27\lib\httplib.py", line 882, in _send_output
    self.send(msg)
  File "C:\Python27\lib\httplib.py", line 844, in send
    self.connect()
  File "C:\Python27\lib\httplib.py", line 821, in connect
    self.timeout, self.source_address)
  File "C:\Python27\lib\socket.py", line 557, in create_connection
    for res in getaddrinfo(host, port, 0, SOCK_STREAM):
IOError: [Errno socket error] [Errno 11001] getaddrinfo failed