code: def _get_ending(self, lookup_url):
          
          if lookup_url.startswith(self.api_server):
              return lookup_url[len(self.api_server) + 1:]
          return lookup_url
docs: Returns the short url ending from a short url or an short url ending.
  
          Example:
           - Given `<your Polr server>/5N3f8`, return `5N3f8`.
           - Given `5N3f8`, return `5N3f8`.
  
          :param lookup_url: A short url or short url ending
          :type lookup_url: str
          :return: The url ending
          :rtype: str