title: Threading using pool and map function
body: <p>Ok so I want to build an app that uses para threads. So I thought Id understand the threading first. I found this <a href="http://chriskiehl.com/article/parallelism-in-one-line/" rel="nofollow">example</a>, for the life of me I cant work out why Im not getting any results back. It doesnt throw any exceptions or anything it just runs and then finishes. Can anyone explain why the below doesnt show any results. I assumed that it was due to not using `print' or return at the end of the function but I played around with that to no avail. Helpss :) please</p>
  
  <pre><code>import urllib2 
  from multiprocessing.dummy import Pool as ThreadPool 
  
  urls = [
      'http://www.python.org', 
      'http://www.python.org/about/',
      'http://www.onlamp.com/pub/a/python/2003/04/17/metaclasses.html',
      'http://www.python.org/doc/',
      'http://www.python.org/download/',
      'http://www.python.org/getit/',
      'http://www.python.org/community/',
      'https://wiki.python.org/moin/',
      'http://planet.python.org/',
      'https://wiki.python.org/moin/LocalUserGroups',
      'http://www.python.org/psf/',
      'http://docs.python.org/devguide/',
      'http://www.python.org/community/awards/'
      # etc.. 
  ]
  
  # Make the Pool of workers
  pool = ThreadPool(4) 
  # Open the urls in their own threads
  # and return the results
  results = pool.map(urllib2.urlopen, urls)
  #close the pool and wait for the work to finish 
  pool.close() 
  pool.join() 
  </code></pre>