def __len__ ( self ):
        return len( self.list )
take the input data_columns and min_itemize and create a data
dataset/ETHPy150Open enthought/traitsui/traitsui/editors/table_editor.py/ReversedList.__len__--crossover with--dataset/ETHPy150Open pydata/pandas/pandas/io/pytables.py/Table.validate_data_columns