old_contents: from __future__ import with_statement
  from hashlib import sha1, sha256
  
  try:
    from urllib.request import urlopen # Python 3
  except ImportError:
    from urllib2 import urlopen # Python 2
  
  def url_to_prefetch(url)
    hashes = sha1(), sha256()
    chunksize = max(4096, max(h.block_size for h in hashes))
    size = 0
    
    response = urlopen(url)
    while True:
      chunk = response.read(chunksize)
      if not chunk:
        break
      f.write(chunk)
  
  
  
  if __name__ == '__main__':
    url_to_prefetch("http://google.com")
  
  # References: 
  #  - https://stackoverflow.com/questions/537542/how-can-i-create-multiple-hashes-of-a-file-using-only-one-pass
  #  - https://stackoverflow.com/questions/1517616/stream-large-binary-files-with-urllib2-to-file
  #  - https://stackoverflow.com/questions/16694907/how-to-download-large-file-in-python-with-requests-py
  #  - https://gist.github.com/Zireael-N/ed36997fd1a967d78cb2
  
new_contents: from __future__ import with_statement
  from hashlib import sha1, sha256
  
  try:
    from urllib.request import urlopen # Python 3
  except ImportError:
    from urllib2 import urlopen # Python 2
  
  def url_to_prefetch(url)
    hashes = sha1(), sha256()
    chunksize = max(4096, max(h.block_size for h in hashes))
    size = 0
    filename = "testfile"
    
    response = urlopen(url)
    while True:
      chunk = response.read(chunksize)
      if not chunk:
        break
      for h in hashes:
        h.update(chunk)
    
    return ""
  
  
  
  if __name__ == '__main__':
    print( url_to_prefetch("http://google.com") )
  
  # References: 
  #  - https://stackoverflow.com/questions/537542/how-can-i-create-multiple-hashes-of-a-file-using-only-one-pass
  #  - https://stackoverflow.com/questions/1517616/stream-large-binary-files-with-urllib2-to-file
  #  - https://stackoverflow.com/questions/16694907/how-to-download-large-file-in-python-with-requests-py
  #  - https://gist.github.com/Zireael-N/ed36997fd1a967d78cb2
  
subject: Update url_to_prefetch.py