def __init__(self, groups=None):
        super(GroupedRequirements, self).__init__(NamedRequirements)
        self.groups = groups or self.default_groups
        self.filename = None
        self.create_default_groups()
def is_overdue(self):
        """
        Returns True when the due date is in the past and the task has not
        yet been completed.
        """
        return not self.is_completed() and self.days_till_due() < 0