使用stack类检查括号( "("，")"，"<"，">“)是否平衡- python

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

    def push(self, item):
        self.stack.append(item)

    def pop(self):
        if not self.is_empty():
            return self.stack.pop()
        return None

    def is_empty(self):
        return len(self.stack) == 0

    def peek(self):
        if not self.is_empty():
            return self.stack[-1]
        return None

def check_balanced_parentheses(expression):
    stack = Stack()
    opening_brackets = ["(", "<"]
    closing_brackets = [")", ">"]
    for char in expression:
        if char in opening_brackets:
            stack.push(char)
        elif char in closing_brackets:
            if stack.is_empty():
                return False
            top = stack.pop()
            if opening_brackets.index(top) != closing_brackets.index(char):
                return False
    return stack.is_empty()

expression = input("请输入一个包含括号的表达式：")
if check_balanced_parentheses(expression):
    print("括号平衡")
else:
    print("括号不平衡")