code: def write_xls(data, file_name, worksheet_names=None):
      '''
      Writes out to old excel format.
  
      Args:
          data: 2D list of tables/worksheets.
          file_name: Name of the output file.
          worksheet_names: A list of worksheet names (optional).
      '''
      workbook = xlwt.Workbook()
      for sheet_index, sheet_data in enumerate(data):
          if worksheet_names and sheet_index < len(worksheet_names) and worksheet_names[sheet_index]:
              name = worksheet_names[sheet_index]
          else:
              name = 'Worksheet {}'.format(sheet_index)
          sheet = workbook.add_sheet(name)
          for row_index, row in enumerate(sheet_data):
              for col_index, value in enumerate(row):
                  sheet.write(row_index, col_index, value)
      workbook.save(file_namef write_xls(data, file_name, worksheet_names=None):
      '''
      Writes out to old excel format.
  
      Args:
          data: 2D list of tables/worksheets.
          file_name: Name of the output file.
          worksheet_names: A list of worksheet names (optional).
      '''
      workbook = xlwt.Workbook()
      for sheet_index, sheet_data in enumerate(data):
          if worksheet_names and sheet_index < len(worksheet_names) and worksheet_names[sheet_index]:
              name = worksheet_names[sheet_index]
          else:
              name = 'Worksheet {}'.format(sheet_index)
          sheet = workbook.add_sheet(name)
          for row_index, row in enumerate(sheet_data):
              for col_index, value in enumerate(row):
                  sheet.write(row_index, col_index, value)
      workbook.save(file_name)
docs: Writes out to old excel format.
  
      Args:
          data: 2D list of tables/worksheets.
          file_name: Name of the output file.
          worksheet_names: A list of worksheet names (optional).