parse datetime from string

script.py

import openpyxl, os, datetime

here = os.path.dirname(os.path.abspath(__file__))
os.chdir(here)
wb = openpyxl.load_workbook("mb51.xlsx")
sheet1 = wb[wb.sheetnames[0]]
date_time_str = sheet1.cell(4,3).value
date_time_obj = datetime.datetime.strptime(date_time_str, '%d.%m.%Y')
print(date_time_obj.isocalendar()[1])