python模块——re模块（简单的计算器功能实现_eval版）

#!/usr/bin/env python
# -*- coding:utf-8 -*-
__author__ = "loki"
 
# Usage: Make a Diy Calculator
# example:
#    '1 - 2 * ((60-30 +(-40/5) * (9-2*5/3+7/3*99/4*2998+10*568/14))-(-4*3)/(16-3*2))'
 
import re
RE_RULE = '\([^()]+\)'
 
def arithmetical(temp):
    result = eval(temp)
    return result
 
def main(arithmetic):
    step = 0
    while 1:
        step += 1
        result = re.search(RE_RULE, arithmetic)
        if result:  # if exist '()'
            temp_ = result.group()
            calc_res = str(arithmetical(temp_))
            arithmetic = re.sub(RE_RULE, calc_res, arithmetic, 1)  # replace  source values, Note!!! must "1" 不然会出现使用相同的结果多次替换
            print(arithmetic, "step: %s" % step)
        else:  # if not '()'
            return arithmetical(arithmetic)
 
if __name__ == '__main__':
    print("result: %s" % (main(user_input)))