code: def fetch_by_refresh_token(self, refresh_token):
          
          row = self.fetchone(self.fetch_by_refresh_token_query, refresh_token)
  
          if row is None:
              raise AccessTokenNotFound
  
          scopes = self._fetch_scopes(access_token_id=row[0])
  
          data = self._fetch_data(access_token_id=row[0])
  
          return self._row_to_token(data=data, scopes=scopes, row=row)
docs: Retrieves an access token by its refresh token.
  
          :param refresh_token: The refresh token of an access token as a `str`.
  
          :return: An instance of :class:`oauth2.datatype.AccessToken`.
  
          :raises: :class:`oauth2.error.AccessTokenNotFound` if not access token
                   could be retrieved.