计算器

import re
s = '2-1*-22-3-4/-5'
def result_small( s ):     #　计算乘除
    if '*' in s:
        a, b = s.split('*')
        return float(a)*float(b)
    elif '/' in s:
        a, b = s.split('/')
        return float(a)/float(b)

def get_small( s ):  #获取乘除最小单位
    while True:
        ret = re.search(r'\d+(\.\d+)?[*/]-?\d+(\.\d+)?', s)
        if ret:
            res = result_small(ret.group())
            s = s.replace(ret.group(), str(res))
        else:
            break
    return s

def get_change(s):   #修正符号
    s = s.replace("--", '+')
    s = s.replace('+-', '-')
    s = s.replace('-+', '-')
    s = s.replace('++', '+')
    return s

def add_sub(s):   # 求和
    ret = re.findall(r'[+-]?\d+(?:\.\d+)?', s)
    sum = 0
    for i in ret:
        sum = sum + float(i)
    return sum

def main(s):    #计算
    s = s.replace(' ', '')
    s = get_small(s)
    s = get_change(s)
    s = add_sub(s)
    return s

def content(s):
    s = s.replace(' ', '')
    while True:
        ret = re.search(r'\([^()]+\)', s)
        if ret:
            reg = str(main(ret.group()))
            print(ret.group(), main(ret.group()))
            s = s.replace(ret.group(), reg)
            s = get_change(s)
        else:
            break
    return main(s)
ret = content("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)
print(eval('1 - 2 * ( (60 - 30 +(-40/ 5) * (9-2 * 5/ 3 + 7 / 3 * 99/ 4 * 2998 + 10 * 568/14 )) - (-4 * 3)/ (16-3*2) )'))

#  先正则匹配到最内层括号，然后计算结果并替换直到没有括号，然后计算乘除，最后计算加减