code: def get_first_of_week(self):
          
          if self.first_of_week is None:
              raise ImproperlyConfigured("%s.first_of_week is required." % self.__class__.__name__)
          if self.first_of_week not in range(7):
              raise ImproperlyConfigured("%s.first_of_week must be an integer between 0 and 6." % self.__class__.__name__)
          return self.first_of_week
docs: Returns an integer representing the first day of the week.
  
          0 represents Monday, 6 represents Sunday.