05正则表达式-计算器的实现

express = '1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )'
# 2776672.6952380957
# eval
# 先算小括号里的
# 再先乘除后加减的计算

#-*-coding:utf-8-*-
__author__ = 'Eva_J'
import re
def cal(exp): # '40/5.3' '2*3'
    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 exp_format(exp):
    exp = exp.replace('--','+')
    exp = exp.replace('++','+')
    exp = exp.replace('-+','-')
    exp = exp.replace('+-','-')
    return exp
def nobracket_exp_handle(no_bracket_exp):
    print('--->',no_bracket_exp)
    while True:
        ret = re.search('\d+(\.\d+)?[*/]-?\d+(\.\d+)?',no_bracket_exp)
        if ret:
            son_exp = ret.group()
            res = cal(son_exp)
            print(res)
            no_bracket_exp = no_bracket_exp.replace(son_exp,res)
            print(no_bracket_exp)
        else:break
    print('-->',no_bracket_exp)
    no_bracket_exp = exp_format(no_bracket_exp)
    ret_lst = re.findall('[+-]?\d+(?:\.\d+)?',no_bracket_exp)
    ret = sum([float(num) for num in ret_lst])
    print('-->',ret)
    return str(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) )'
# 去掉空格
express = express.replace(' ','')
print(express)
# 匹配出最内部的括号的表达式
while True:
    ret = re.search('\([^()]+\)',express)
    if ret:
        no_bracket_exp = ret.group()
        print(no_bracket_exp)
        # 先算乘除 先把乘除法匹配出来
        # 乘除法 不匹配第一个数字的负号
        res = nobracket_exp_handle(no_bracket_exp)
        express = express.replace(no_bracket_exp,res)
        express = exp_format(express)
    else:break
ret = nobracket_exp_handle(express)
print(ret)

 

# 'a*b'

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