code: def add(reader, writer, column, start, stop, value):
    
    for i, row in enumerate(reader):
      if i >= start and i <= stop:
        row[column] = type(value)(row[column]) + value
      writer.appendRecord(row)
docs: Adds a value over a range of rows.
  
    Args:
      reader: A FileRecordStream object with input data.
      writer: A FileRecordStream object to write output data to.
      column: The column of data to modify.
      start: The first row in the range to modify.
      end: The last row in the range to modify.
      value: The value to add.