import xlrd, xlwt
from xlutils.copy import copy as xl_copy
# open existing workbook
rb = xlrd.open_workbook('ex.xls', formatting_info=True)
# make a copy of it
wb = xl_copy(rb)
# add sheet to workbook with existing sheets
Sheet1 = wb.add_sheet('Sheet_apend')
wb.save('ex.xls')