[Tutor] Question about urllib module?

[libsvm]

Dear all, 

I was learning how to use the urllib, BUT there is nothing printed out
in the following example.
Could anyone hellp me or tell why?

  import urllib
  params = urllib.urlencode({'DN':'Adrenal glands disorders'})
  address="http://xin.cz3.nus.edu.sg/group/cjttd/List.asp?SetQuery=Y"
  f = urllib.urlopen(address,params)
  print f.read()

Regards,
Denny