code: def is_not_modified(
          self, response_headers: Headers, request_headers: Headers
      ) -> bool:
          
          try:
              if_none_match = request_headers["if-none-match"]
              etag = response_headers["etag"]
              if if_none_match == etag:
                  return True
          except KeyError:
              pass
  
          try:
              if_modified_since = parsedate(request_headers["if-modified-since"])
              last_modified = parsedate(response_headers["last-modified"])
              if (
                  if_modified_since is not None
                  and last_modified is not None
                  and if_modified_since >= last_modified
              ):
                  return True
          except KeyError:
              pass
  
          return False
docs: Given the request and response headers, return `True` if an HTTP
          "Not Modified" response could be returned instead.