#!/usr/bin/env python# ---------------------------------------# author : Geng Jie# email  : gengjie@outlook.com# Create Time: 2016/3/16 23:38# ----------------------------------------class Node:    def __init__(self, value):        self.value = value        self.next = Noneclass Stack:    def __init__(self):        self.top = None    def push(self, value):        node = Node(value)        node.next = self.top        self.top = node    def pop(self):        node = self.top        self.top = node.next        return node.valueif __name__ == '__main__':    stack = Stack()    # for i in range(10):    #     stack.push(i)    #     # while stack.top:    #     #     print(stack.pop())    exp = '{a * [x/(x+y)]}'    for c in exp:        if c in '{[(':            stack.push(c)        elif c in '}])':            v = stack.top.value            if c == '}' and v != '{':                raise Exception('failed')            if c == ']' and v != '[':                raise Exception('failed')            if c == ')' and v != '(':                raise Exception('failed')            stack.pop()    if stack.top is not None:        raise Exception('failed')    print('ok')