实现计算器

实现能计算类似 
1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )等类似公式的计算器程序

# -*- encoding:utf-8 -*-
import re


def dealwith(exp):
    exp = exp.replace("+-", '-')
    exp = exp.replace("--", '+')
    return exp


def cal_exp_son(exp_son):
    if '/' in exp_son:
        a, b = exp_son.split('/')
        return str(float(a)/float(b))
    elif '*' in exp_son:
        a, b = exp_son.split('*')
        return str(float(a)*float(b))


def cal_express_no_bracker(exp):
    exp = exp.strip("()")
    while True:
        ret = re.search('d+.?d*[*/]-?d+.?d*', exp)
        if ret:
            exp_son = ret.group()
            ret = cal_exp_son(exp_son)
            exp = exp.replace(exp_son,ret)
            exp = dealwith(exp)
        else:
            ret = re.findall('-?d+.?d*', exp)
            sum = 0
            for i in ret:
                sum += float(i)
            return str(sum)


def remove_bracket(new_express):
    """
    提取括号里没有其他括号的表达式
    :param new_express: 表达式字符串
    :return: 表达式计算的结果
    """
    while True:
        ret = re.search('([^()]+)', new_express)   # 查找最内层含有括号的
        if ret:
            express_no_bracker = ret.group()
            ret = cal_express_no_bracker(express_no_bracker)  # 计算括号里的结果
            exp = new_express.replace(express_no_bracker, ret)
            new_express = dealwith(exp)
        else:
            ret = cal_express_no_bracker(new_express)
            return ret


express = '1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )'

# 去空格
new_express = express.replace(' ', '')
result = remove_bracket(new_express)
print(result)