def clear(self):
        super(GroupedRequirements, self).clear()
        self.create_default_groups()
def is_active(self):
        """
        Returns True when the start date is today or in the past and the
        task has not yet been completed.
        """
        start = self.start_date()
        return not self.is_completed() and (not start or start <= date.today())