code: def list_comments(self, topic_id, start=0):
          
          xml = self.api.xml(API_GROUP_GET_TOPIC % topic_id, params={'start': start})
          xml_results = xml.xpath('//ul[@id="comments"]/li')
          results = []
          for item in xml_results:
              try:
                  author_avatar = item.xpath('.//img/@src')[0]
                  author_url = item.xpath('.//div[@class="user-face"]/a/@href')[0]
                  author_alias = slash_right(author_url)
                  author_signature = item.xpath('.//h4/text()')[1].strip()
                  author_nickname = item.xpath('.//h4/a/text()')[0].strip()
                  created_at = item.xpath('.//h4/span/text()')[0].strip()
                  content = etree.tostring(item.xpath('.//div[@class="reply-doc content"]/p')[0]).decode('utf8').strip()
                  cid = item.get('id')
                  results.append({
                      'id': cid,
                      'author_avatar': author_avatar,
                      'author_url': author_url,
                      'author_alias': author_alias,
                      'author_signature': author_signature,
                      'author_nickname': author_nickname,
                      'created_at': created_at,
                      'content': unescape(content),
                  })
              except Exception as e:
                  self.api.logger.exception('parse comment exception: %s' % e)
          return build_list_result(results, xml)
docs: 回复列表
          
          :param topic_id: 话题ID
          :param start: 翻页
          :return: 带下一页的列表