def close(self):
		'''关闭与数据库的连接'''
		if VERBOSE:
			print 'Database connection CLOSE.'
		self.conn.close()
def get_leafs(self):
		if self.lchild == None and self.rchild == None:
			return [self.leaf]
		else:
			return self.lchild.get_leafs()+self.rchild.get_leafs()