开发一个简单的Python计算器

# -*- coding:utf-8 -*-
# @Time    : 2019/x/x
# @Author  : root
 
import re
 
 
operatorDict = {
    '+': lambda a, b: float(a) + float(b),
    '-': lambda a, b: float(a) - float(b),
    '*': lambda a, b: float(a) * float(b),
    '/': lambda a, b: float(a) / float(b),
}
 
def calculator(expression='1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + '
                          '7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )'):
    '''
    计算器
    总逻辑：
        1.先找出内层括号，然后计算其内的终值，用终值替换原表达式
        2.然后重复以上过程
    无括号部分计算逻辑:
        1.先截断为数字和运算符的列表，数字可包含负号；
        2.运算列表中的值并替换，先乘除后加减；
    :param expression: 字符串表达式
    :return:表达式计算值
    '''
 
    print("正确答案为： ",eval(expression))
 
 
    def calWithOutBrackets(expression='-1+2*3/4-5*-3'):
        # 截断为数字和运算符的列表
        for i in operatorDict:
            expression = expression.replace(i,'s'+i+'s')
        l =expression.split('s')
        l2 = []
        i =0
        while i <len(l):
            if l[i] == '':
                l2.append(l[i+1]+l[i+2])
                i +=2
            else:
                l2.append(l[i])  # 不带负号的数字和运算符
            i += 1
        # 运算乘除
        i = 1
        while i<len(l2):
            if l2[i] in ['*','/']:
                l2[i-1:i+2] = [operatorDict[l2[i]](l2[i-1],l2[i+1])]
            else:
                i+=2
        # 运算加减
        while len(l2)>1:
            l2[0:3] = [operatorDict[l2[1]](l2[0], l2[2])]
        return str(l2[0])
 
    expression=expression.replace(' ','')
    check = re.search('\([^\(\)]+\)', expression)
    while check:
        checkValue = check.group()
        # print(checkValue)
        expression = expression.replace(checkValue, calWithOutBrackets(checkValue[1:-1]))
        check = re.search('\([^\(\)]*\)', expression)
    else:
        return calWithOutBrackets(expression)
 
 
if __name__ == '__main__':
    re = calculator()
    print("实际结果为： ",re)