code: def urlsafe(self):
      
      # This is 3-4x faster than urlsafe_b64decode()
      urlsafe = base64.b64encode(self.reference().Encode())
      return urlsafe.rstrip('=').replace('+', '-').replace('/', '_')
docs: Return a url-safe string encoding this Key's Reference.
  
      This string is compatible with other APIs and languages and with
      the strings used to represent Keys in GQL and in the App Engine
      Admin Console.