如何使用堆栈(push、pop、top)向后存储和输出字符串？

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()

    def top(self):
        if not self.is_empty():
            return self.stack[-1]

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

def reverse_string(input_string):
    stack = Stack()
    output_string = ""

    # 将字符串按字符顺序进行push操作
    for char in input_string:
        stack.push(char)

    # 通过pop操作逆序输出字符串
    while not stack.is_empty():
        output_string += stack.pop()

    return output_string

# 示例用法
input_string = "Hello, World!"
output_string = reverse_string(input_string)
print(output_string)  # 输出：!dlroW ,olleH