Python 用栈判断括号匹配

#!/usr/bin/python
# -*- coding: UTF-8 -*-

from pythonds.basic.stack import Stack
def parChecker(symbolString):
    s = Stack()
    balanced = True
    index = 0
    while index < len(symbolString) and balanced:
        symbol =symbolString[index]
　　　　　#左边括号入栈
        if symbol == '(':
            s.push(symbol)
        else:
　　　　　　　#如果栈提前为空，则表示前面匹配成功，后面没有匹配成功
            if s.isEmpty():
                balanced = False
　　　　　　　#右边括号出栈
            else:
                s.pop()

        index += 1
if balanced and s.isEmpty():
        return True
    else:
        return False

print(parChecker('()())'))
print(parChecker('()()()'))
print(parChecker('((()())())'))