Retrieve the value at the given coordinates.

        Parameters
        ----------
        sid : int
            The asset identifier.
        dt : pd.Timestamp
            The timestamp for the desired data point.
        field : string
            The OHLVC name for the desired data point.

        Returns
        -------
        value : float|int
            The value at the given coordinates, ``float`` for OHLC, ``int``
            for 'volume'.

        Raises
        ------
        NoDataOnDate
            If the given dt is not a valid market minute (in minute mode) or
            session (in daily mode) according to this reader's tradingcalendar.

def get_value(self, sid, dt, field):
        """
        Retrieve the value at the given coordinates.

        Parameters
        ----------
        sid : int
            The asset identifier.
        dt : pd.Timestamp
            The timestamp for the desired data point.
        field : string
            The OHLVC name for the desired data point.

        Returns
        -------
        value : float|int
            The value at the given coordinates, ``float`` for OHLC, ``int``
            for 'volume'.

        Raises
        ------
        NoDataOnDate
            If the given dt is not a valid market minute (in minute mode) or
            session (in daily mode) according to this reader's tradingcalendar.
        """
        self._validate_assets([sid])
        self._validate_timestamp(dt)

        sid_ix = self.sids.searchsorted(sid)
        dt_ix = self.dates.searchsorted(dt.asm8)

        value = self._postprocessors[field](
            self._country_group[DATA][field][sid_ix, dt_ix]
        )

        # When the value is nan, this dt may be outside the asset's lifetime.
        # If that's the case, the proper NoDataOnDate exception is raised.
        # Otherwise (when there's just a hole in the middle of the data), the
        # nan is returned.
        if np.isnan(value):
            if dt.asm8 < self.asset_start_dates[sid_ix]:
                raise NoDataBeforeDate()

            if dt.asm8 > self.asset_end_dates[sid_ix]:
                raise NoDataAfterDate()

        return value