反向波兰记法Calc:两个返回减号的正数的减法？

def rpn_calculator(expression):
    stack = []
    tokens = expression.split()
    
    for token in tokens:
        if token.isdigit():
            stack.append(int(token))
        else:
            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(a / b)
    
    return stack[0]

# 示例使用
expression = "5 3 -"
result = rpn_calculator(expression)
print(f"The result of {expression} is {result}")

if len(stack) < 2:
    raise ValueError("Not enough operands for the operator")