how can I extract all urls in a string by using re.findall() ?

[could ildg]

I want to retrieve all urls in a string. When I use re.fiandall, I get
a list of tuples.
My code is like below:

url=unicode(r"((http|ftp)://)?(((([\d]+\.)+){3}[\d]+(/[\w./]+)?)|([a-z]\w*((\.\w+)+){2,})([/][\w.~]*)*)")
m=re.findall(url,html)
for i in m:
   print i

html is a variable of string type which contains many urls in it.
the code will print many tuples, and each tuple seems not to represent
a url. e.g, one of them is as below:

(u'http://', u'http', u'image.zhongsou.com/image/netchina.gif', u'',
u'', u'', u'', u'image.zhongsou.com', u'.com', u'.com',
u'/netchina.gif')

Why is there two "http" in it? and why are there so many ampty strings
in the tupe above? It's obviously not a url. How can I get the urls
correctly?

Thanks in advance.