code: def on_change_checkout(self):
          '''
          When you change checkout or checkin update dummy field
          -----------------------------------------------------------
          @param self: object pointer
          @return: raise warning depending on the validation
          '''
          checkout_date = time.strftime(dt)
          checkin_date = time.strftime(dt)
          if not (checkout_date and checkin_date):
              return {'value': {}}
          delta = timedelta(days=1)
          dat_a = time.strptime(checkout_date, dt)[:5]
          addDays = datetime(*dat_a) + delta
          self.dummy = addDays.strftime(dtf on_change_checkout(self):
          '''
          When you change checkout or checkin update dummy field
          -----------------------------------------------------------
          @param self: object pointer
          @return: raise warning depending on the validation
          '''
          checkout_date = time.strftime(dt)
          checkin_date = time.strftime(dt)
          if not (checkout_date and checkin_date):
              return {'value': {}}
          delta = timedelta(days=1)
          dat_a = time.strptime(checkout_date, dt)[:5]
          addDays = datetime(*dat_a) + delta
          self.dummy = addDays.strftime(dt)
docs: When you change checkout or checkin update dummy field
          -----------------------------------------------------------
          @param self: object pointer
          @return: raise warning depending on the validation