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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_ending(self, lookup_url):
 """ 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 """

        if lookup_url.startswith(self.api_server):
            return lookup_url[len(self.api_server) + 1:]
        return lookup_url