quickly recover HTML code of several URL?

[Jack]

I want simultaneously to recover HTML code of a list of URL. (tread, 
threading modules ?)
and write the result in a file (use mutex ?).
Can someone modify my code, or help me ?
thanks
---
import urllib
URLs = 
["http://www.google.com","http://www.debian.org","http://www.python.org"]
def getHtmlSource(url):
	htmlSource = urllib.urlopen(url).read()
	fichier = open('test.txt', 'a')
	fichier.write(htmlSource)
	fichier.close()
for url in URLs:
     getHtmlSource(url)