def release_ids(self):
        """
            >>> package = yarg.get('yarg')
            >>> package.release_ids
            [u'0.0.1', u'0.0.5', u'0.1.0']
        """
        r = [(k, self._releases[k][0]['upload_time'])
             for k in self._releases.keys()
             if len(self._releases[k]) > 0]
        return [k[0] for k in sorted(r, key=lambda k: k[1])]