我正在努力反向迭代输入，以创建一个普通的波兰语符号计算器

def evaluate_rpn(tokens):
    stack = []
    for token in tokens:
        if token in ['+', '-', '*', '/']:
            b = stack.pop()
            a = stack.pop()
            if token == '+':
                stack.append(a + b)
            elif token == '-':
                stack.append(a - b)
            elif token == '*':
                stack.append(a * b)
            elif token == '/':
                stack.append(int(a / b))  # 使用int()来确保结果是整数
        else:
            stack.append(int(token))
    return stack[0]

# 示例输入
expression = "3 4 + 2 * 7 /"
result = evaluate_rpn(expression.split())
print(f"The result of the expression '{expression}' is {result}")