#!/usr/bin/env python
import datetime as DT
from openpyxl import Workbook
from openpyxl.styles import NamedStyle

workbook = Workbook()
worksheet = workbook.active
dt = worksheet.cell(row=1, column=1).value = DT.date.today()

cell = worksheet.cell(row=1, column=2)
cell.value = dt  # same value
my_date_style = NamedStyle(name='my_date_style', number_format='dd.mm.yyyy')
cell.style = my_date_style  # different style
workbook.save('book.xlsx')