Parameters
        ----------
        columns : list of str
           'open', 'high', 'low', 'close', or 'volume'
        start_date: Timestamp
           Beginning of the window range.
        end_date: Timestamp
           End of the window range.
        assets : list of int
           The asset identifiers in the window.

        Returns
        -------
        list of np.ndarray
            A list with an entry per field of ndarrays with shape
            (minutes in range, sids) with a dtype of float64, containing the
            values for the respective field over start and end dt range.

def load_raw_arrays(self,
                        columns,
                        start_date,
                        end_date,
                        assets):
        """
        Parameters
        ----------
        columns : list of str
           'open', 'high', 'low', 'close', or 'volume'
        start_date: Timestamp
           Beginning of the window range.
        end_date: Timestamp
           End of the window range.
        assets : list of int
           The asset identifiers in the window.

        Returns
        -------
        list of np.ndarray
            A list with an entry per field of ndarrays with shape
            (minutes in range, sids) with a dtype of float64, containing the
            values for the respective field over start and end dt range.
        """
        country_code = self._country_code_for_assets(assets)

        return self._readers[country_code].load_raw_arrays(
            columns,
            start_date,
            end_date,
            assets,
        )