def close(self):
		'''关闭与数据库的连接'''
		if VERBOSE:
			print 'Database connection CLOSE.'
		self.conn.close()
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