使用python实现简易计算器-支持加减乘除和括号

priority_dict = {  # 操作符优先级字典 
    "+": 1, 
    "-": 1, 
    "*": 2, 
    "/": 2 
} 
 
operands_dict = {  # 操作符函数字典 
    "+": lambda x, y: x + y, 
    "-": lambda x, y: x - y, 
    "*": lambda x, y: x * y, 
    "/": lambda x, y: x / y, 
} 
 
 
def calculator(expression): 
    suffix = _infix2suffix(expression) 
    return _calsuffix(suffix) 
 
 
def _calsuffix(suffix): 
    ''' 
    计算后缀表达式 
    :param suffix: 后缀表达式 
    :return: 
    ''' 
    stack = [] 
    for item in list(suffix): 
        ''' 
        是数字，入栈 
        是操作符，出栈2个，计算，入栈 
        ''' 
        if item.isdecimal(): 
            stack.append(item) 
        elif item in operands_dict.keys(): 
            num2 = float(stack.pop()) 
            num1 = float(stack.pop()) 
            stack.append(operands_dict[item](num1, num2)) 
        else: 
            raise KeyError("illegal expression") 
    if len(stack) != 1: 
        raise KeyError("illegal expression") 
    return stack.pop() 
 
 
def _infix2suffix(expression): 
    ''' 
    中缀表达式转后缀表达式 
    :param expression: 中缀表达式 
    :return: 后缀表达式 
    ''' 
    result = []  # 结果列表 
    stack = []  # 栈 
    for item in expression: 
        ''' 
        是数字，直接添加到结果列表 
        是左括号，入栈 
        是右括号，依次出栈，直到左括号 
        是操作符，栈为空或栈顶为左括号或当前操作符比栈顶操作符优先级高，直接入栈 
                其他情况，依次出栈，直到栈为空或栈顶为左括号或当前操作符比栈顶操作符优先级高，当前操作符入栈 
        ''' 
        if item.isdecimal(): 
            result.append(item) 
        else: 
            if item == "(": 
                stack.append(item) 
            elif item == ")": 
                while True: 
                    if len(stack) == 0: 
                        raise KeyError("illegal expression") 
                    pop_item = stack.pop() 
                    if pop_item == "(": 
                        break 
                    result.append(pop_item) 
            elif item in priority_dict.keys(): 
                if len(stack) == 0 or \ 
                        stack[len(stack) - 1] == "(" or \ 
                        priority_dict[item] > priority_dict[stack[len(stack) - 1]]: 
                    stack.append(item) 
                else: 
                    while True: 
                        if len(stack) == 0 or \ 
                                stack[len(stack) - 1] == "(" or \ 
                                priority_dict[item] > priority_dict[stack[len(stack) - 1]]: 
                            break 
                        result.append(stack.pop()) 
                    stack.append(item) 
            else: 
                raise KeyError("illegal expression") 
    while len(stack) > 0: 
        result.append(stack.pop()) 
    return "".join(result) 
 
if __name__ == "__main__": 
    print(calculator("1+2/(3*3-5)*3"))  # 1233*5-/3*+