code: def column_list(string):
      
      try:
          columns = list(map(int, string.split(',')))
      except ValueError as e:
          raise argparse.ArgumentTypeError(*e.args)
      for column in columns:
          if column < 1:
              raise argparse.ArgumentTypeError(
                  'Invalid column {!r}: column numbers start at 1.'
                  .format(column))
      return columns
docs: Validate and convert comma-separated list of column numbers.