计算机功能简单实现

import  re
def  atom_cal(exp):
    if "*" in exp:
        a, b = exp.split("*")
        return str(float(a)*float(b))
    elif "/" in exp:
        a, b = exp.split("/")
        return str(float(a) / float(b))

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

def mul_div(exp):
    while True:
        ret = re.search("d+(.d+)?[*/]-?d+(.d+)?", exp)
        if ret:
            atom_exp = ret.group()
            res = atom_cal(atom_exp)
            exp = exp.replace(atom_exp, res)

        else:
            return exp

def add_sub(exp):
    ret = re.findall("[+-]?d+(?:.d+)?", exp)
    exp_sum = 0
    for i in ret:
        exp_sum += float(i)
    return exp_sum


def cal(exp):
    exp = mul_div(exp)
    exp = format_exp(exp)
    exp_sum = add_sub(exp)
    return exp_sum
ret = cal('1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) ')
print(ret)