code: def add_days(date_obj, days_int):
          
          n = from_ymd_to_excel(*date_obj.date) + days_int
  
          return BaseDateTuple(*from_excel_to_ymd(n))
docs: addition of a number of days
  
          :param BaseDateTuple d:
          :param int days_int:
          :return BaseDatetimeDate: