code: def is_correct(self):
          
          valid = self.day in Daterange.weekdays
          if not valid:
              logger.error("Error: %s is not a valid day", self.day)
          # Check also if Daterange is correct.
          valid &= super(StandardDaterange, self).is_correct()
          return valid
docs: Check if the Daterange is correct : weekdays are valid
  
          :return: True if weekdays are valid, False otherwise
          :rtype: bool