class ColInsertFilter(Filter):

    '''Adds a column to each row

    @param mk_value(row, row_num)

    '''

    def __init__(self, reader, mk_value, index=0):

        def filter_(row):

            row = list(row) # make sure it's mutable; don't modify input!

            row.insert(index, mk_value(row, self.reader.line_num))

            return row

        Filter.__init__(self, filter_,

            streams.LineCountInputStream(StreamFilter(reader)))