Get hashes of urls in file.

def _get_url_hashes(path):
  """Get hashes of urls in file."""
  urls = _read_text_file(path)
  def url_hash(u):
    h = hashlib.sha1()
    try:
      u = u.encode('utf-8')
    except UnicodeDecodeError:
      logging.error('Cannot hash url: %s', u)
    h.update(u)
    return h.hexdigest()
  return {url_hash(u): True for u in urls}