code: def _get_daily_window_data(self,
                                 assets,
                                 field,
                                 days_in_window,
                                 extra_slot=True):
          
          bar_count = len(days_in_window)
          # create an np.array of size bar_count
          dtype = float64 if field != 'sid' else int64
          if extra_slot:
              return_array = np.zeros((bar_count + 1, len(assets)), dtype=dtype)
          else:
              return_array = np.zeros((bar_count, len(assets)), dtype=dtype)
  
          if field != "volume":
              # volumes default to 0, so we don't need to put NaNs in the array
              return_array[:] = np.NAN
  
          if bar_count != 0:
              data = self._history_loader.history(assets,
                                                  days_in_window,
                                                  field,
                                                  extra_slot)
              if extra_slot:
                  return_array[:len(return_array) - 1, :] = data
              else:
                  return_array[:len(data)] = data
          return return_array
docs: Internal method that gets a window of adjusted daily data for a sid
          and specified date range.  Used to support the history API method for
          daily bars.
  
          Parameters
          ----------
          asset : Asset
              The asset whose data is desired.
  
          start_dt: pandas.Timestamp
              The start of the desired window of data.
  
          bar_count: int
              The number of days of data to return.
  
          field: string
              The specific field to return.  "open", "high", "close_price", etc.
  
          extra_slot: boolean
              Whether to allocate an extra slot in the returned numpy array.
              This extra slot will hold the data for the last partial day.  It's
              much better to create it here than to create a copy of the array
              later just to add a slot.
  
          Returns
          -------
          A numpy array with requested values.  Any missing slots filled with
          nan.