'Get the colname from daily_bar_table and read all of it into memory,
caching the result.
Parameters
colname : string
A name of a OHLCV carray in the daily_bar_table
Returns
array (uint32)
Full read array of the carray in the daily_bar_table with the
given colname.'

def _spot_col(self, colname):

    try:
        col = self._spot_cols[colname]
    except KeyError:
        col = self._spot_cols[colname] = self._table[colname]
    return col
