code: def _visit_detailpage(self, detailpage_link, referer):
          
          headers = {'Referer': referer}
          res = self.session.get(detailpage_link, headers=headers)
          referer = res.url
          doc = res.content
          result = self._parse_detailpage_html(doc)
          return result, referer
docs: 访问字幕详情页面，解析出下载页面的地址