python中缀表达式转后缀并解出结果的代码

在Python中，我们可以使用栈数据结构来实现中缀表达式到后缀（逆波兰）表达式的转换，然后使用递归计算求值。以下是一个简单的实现：

def infix_to_postfix(expression):
    prec = {'+': 1, '-': 1, '*': 2, '/': 2, '^': 3}  # 运算符优先级
    output = []  # 后缀表达式列表
    op_stack = []  # 运算符栈

    for char in expression:
        if char.isdigit():
            output.append(char)  # 数字直接添加
        elif char == '(':
            op_stack.append(char)
        elif char == ')':
            while op_stack and op_stack[-1] != '(':
                output.append(op_stack.pop())
            op_stack.pop()  # 出栈左括号
        else:  # 遇到运算符
            while (op_stack and op_stack[-1]]):  # 当前运算符比栈顶小或相等，则先出栈
                output.append(op_stack.pop())
            op_stack.append(char)  # 将当前运算符压入栈

    while op_stack:  # 右括号已处理完，再将剩余运算符出栈
        output.append(op_stack.pop())

    return ''.join(output)

def evaluate postfix_expression(postfix_exp):
    stack = []
    for char in postfix_exp:
        if char.isdigit():
            stack.append(int(char))
        else:
            val2 = stack.pop()
            val1 = stack.pop()
            result = apply_operator(val1, val2, char)
            stack.append(result)
    return stack[0]

def apply_operator(val1, val2, operator):
    if operator == '+':
        return val1 + val2
    elif operator == '-':
        return val1 - val2
    elif operator == '*':
        return val1 * val2
    elif operator == '/':
        return val1 / val2
    elif operator == '^':
        return val1 ** val2

# 示例
expression = "3+5*(2^(4+9))"
postfix = infix_to_postfix(expression)
print(f"Postfix expression: {postfix}")
result = evaluate(postfix)
print(f"Result of the expression: {result}")