栈：Stack

1.action

Stack() ：初始化空栈
push(item) ： 栈顶插入
pop() ：栈顶弹出
peek() ：返回栈顶元素
isEmpty() ：判断是否为空
size() ：栈元素数

2.code of python

class Stack:
    def __init__(self):
        self.items = []

    def isEmpty(self):
        return self.items == []
    
    def push(self, item):
        return self.items.append(item)
    
    def pop(self):
        return self.items.pop()
    
    def peek(self):
        return self.items[len(self.items)-1]
    
    def size(self):
        return len(self.items)

3.应用：括号匹配

from stack import Stack

def parChecker(symbolString):
    s = Stack()
    index = 0
    balanced = True
    while index < len(symbolString) and balanced:
        symbol = symbolString[index]
        if symbol == "(":
            s.push(symbol)
        else:
            if s.isEmpty():
                balanced = False
            else:
                s.pop()
        index += 1
    if balanced and s.isEmpty():
        return True
    else:
        return False

print(parChecker("()()(())"))
print(parChecker("(((())"))