def insertDomain(self, domain, indegree=0, outdegree=0):
		'''增加一个域名'''
		cur = self.conn.cursor()
		cur.execute("INSERT INTO Domains VALUES (NULL,?,?,?)", (domain, indegree, outdegree))
		# 写入到文件中
		self.conn.commit()
def dfs_print(root):
        if root is None:
            return
        dfs_print(root.left)
        print(str(root.key) + ' ', end='')
        dfs_print(root.right)