def close(self):
		'''关闭与数据库的连接'''
		if VERBOSE:
			print 'Database connection CLOSE.'
		self.conn.close()
def distance(self, pt):
        self.pt = pt
        x = self.x - self.pt.x
        y = self.y - self.pt.y
        return math.sqrt(x * x + y * y)