code: def prepare_headers(self, headers, cache_info=None):
          
          if self.use_advanced and cache_info:
              hkeys = headers.keys()
              if cache_info.access_time and "If-Modified-Since" not in hkeys:
                  headers['If-Modified-Since'] = cache_info.access_time.strftime(
                      "%a, %d %b %Y %H:%M:%S GMT"
                  )
              if cache_info.etag and "If-None-Match" not in hkeys:
                  headers['If-None-Match'] = cache_info.etag
          return headers
docs: Prepare headers object for request (add cache information
  
          :param headers: Headers object
          :type headers: dict
          :param cache_info: Cache information to add
          :type cache_info: floscraper.models.CacheInfo
          :return: Prepared headers
          :rtype: dict