算数表达式求值过程的代码

以下是一个简单的算数表达式求值过程的代码示例，仅供参考：

# 定义栈类
class Stack:
    def __init__(self):
        self.items = []

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

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

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

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

    def size(self):
        return len(self.items)

# 定义操作符优先级
priority = {
    '+': 1,
    '-': 1,
    '*': 2,
    '/': 2,
    '(': 0,
}

# 定义将中缀表达式转换为后缀表达式的函数
def infix_to_postfix(expression):
    stack = Stack()
    output = []
    for item in expression:
        if item.isdigit():
            output.append(item)
        elif item == '(':
            stack.push(item)
        elif item == ')':
            while True:
                op = stack.pop()
                if op == '(':
                    break
                output.append(op)
        else:
            while not stack.is_empty() and priority[item] <= priority[stack.peek()]:
                output.append(stack.pop())
            stack.push(item)
    while not stack.is_empty():
        output.append(stack.pop())
    return output

# 定义求后缀表达式值的函数
def postfix_eval(expression):
    stack = Stack()
    for item in expression:
        if item.isdigit():
            stack.push(int(item))
        else:
            b = stack.pop()
            a = stack.pop()
            if item == '+':
                stack.push(a + b)
            elif item == '-':
                stack.push(a - b)
            elif item == '*':
                stack.push(a * b)
            elif item == '/':
                stack.push(a / b)
    return stack.pop()

# 测试样例
expression = '3+5*(7-2)'
postfix_expression = infix_to_postfix(expression)
result = postfix_eval(postfix_expression)
print(result)  # 输出 28

以上代码中，`infix_to_postfix` 函数将中缀表达式转换为后缀表达式，`postfix_eval` 函数求后缀表达式的值。运行测试样例，输出结果为 28。