python学习笔记(36) 计算器

要求：

首先得到一个字符串

去空格

找括号，且括号里没有其他括号

从左到右找到第一个乘除法

加减法

只剩一个数了，结束

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import re


def cal_exp_son(exp_son):
    #计算原子型表达式乘除法
    if '/' in exp_son:
        a,b = exp_son.split('/')
        return str(float(a)/float(b))
    elif '*' in exp_son:
        a,b = exp_son.split('*')
        return str(float(a)*float(b))


def clean(express):
    #处理'+-'和'--'符号
    express = express.replace('+-','-')
    express = express.replace('--','+')
    return express


def cal_express_clean(exp):
    #计算没有括号的表达式
    exp = exp.strip('()')
    while 1:
        ret = re.search('\d+\.?\d*[*/]-?\d+\.?\d*',exp)
        if ret:
            exp_son = ret.group()
            ret = cal_exp_son(exp_son)
            exp = exp.replace(exp_son,ret)
            exp = clean(exp)
        else:
            ret = re.findall('-?\d+\.?\d*',exp)
            sum = 0
            for i in ret:
                sum += float(i)
            return str(sum)



def rm_bracket(new_express):
    while 1:
        ret = re.search('\([^()]+\)',new_express)
        if ret:
            express_clean = ret.group()
            # express_clean = express_clean.strip('()')
            ret1 = cal_express_clean(express_clean)
            new_express = new_express.replace(express_clean,ret1)
            new_express = clean(new_express)
            print(new_express)
        else:
            ret = cal_express_clean(new_express)
            return (ret)
            break


express = '1  - 2*((60-30 +(-40/5)*(9-2*5/3+7 /3*99/4*2998 +10*568/14))- (-4*3)/(16-3/2))'
new_express = express.replace(' ','')
res = rm_bracket(new_express)
print(res)