[Chicago] how to use multithread to download?

[守株待兔]

i have written a program to download an online book:
http://www.network-theory.co.uk/docs/pytut/

import time
import urllib
import lxml.html
import os
time1=time.time()
os.mkdir('/tmp/python')
down='http://www.network-theory.co.uk/docs/pytut/'
file=urllib.urlopen(down).read()
root=lxml.html.fromstring(file)
tnodes = root.xpath("//div[@class='main']//ul/li/a")
for x in tnodes:
      url='http://www.network-theory.co.uk/docs/pytut/'+x.get('href')
      name=x.text
      myfile=open('/tmp/python/'+name,'a')
      page=urllib.urlopen(url).read()
      myfile.write(page)
      myfile.close()
time2=time.time()
print  time2-time1

it's slow , would  you  mind to revise it with multithread??
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