A simple example of adding cell comments to a worksheet. For more details see Working with Cell Comments.
Code:
###############################################################################
#
# An example of writing cell comments to a worksheet using Python and
# XlsxWriter.
#
# For more advanced comment options see comments2.py.
#
# Copyright 2013, John McNamara, jmcnamara@cpan.org
#
from xlsxwriter.workbook import Workbook
workbook = Workbook('comments1.xlsx')
worksheet = workbook.add_worksheet()
worksheet.write('A1', 'Hello')
worksheet.write_comment('A1', 'This is a comment')
workbook.close()