正则表达式匹配求值

import re#导入正则库
a = "1 - 2 * ((60 - 30 + (-40.0/5) * (9-2*5/5 + 7 /3*99/4*2998 + 10 * 568/14 )) - (-4*3)/(16 - 3*2) )"
def qiuzhi(tt):
    u = eval(tt)#应用到eval函数，自动字符串求值
    return u
while True:
    r = re.split("\(([^()]+)\)",a ,1)#在a里，以最里面的括号为分割标准，分割一次
    print(r)
    if len(r) == 3:
        bef = r[0]
        mid = r[1]
        aft = r[2]
        n = qiuzhi(mid)
        a = bef + str(n) + aft
        print(mid)
    else:
        final = qiuzhi(a)
        print(final)
        break