code: def get_value(self, sid, dt, field):
          
          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
docs: 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.