python实现加减乘除计算器

需求：

实现加减乘除及拓号优先级解析

用户输入 1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )等类似公式后，必须自己解析里面的(),+,-,*,/符号和公式

注意：不能调用eval等类似功能偷懒实现

分割线：

# -*- coding: utf-8 -*-

# @Time : 2018/10/26 22:00

# @Author : 赵伟江

importre

my_count ='1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )'

my_count = re.sub("\ ","",my_count)#去除字符串中所有空格

# print(my_count)

bracket = re.compile("\(([^()]+)\)")#选出最内部的括号

mul_sub = re.compile("(-?\d+)(\.\d+)?(\*-)(\d+)(\.\d+)?")#选出 a*(-b)

dev_sub = re.compile("(-?\d+)(\.\d+)?(/-)(\d+)(\.\d+)?")#选出 a/(-b)

defadd_sub(arg):

'''

将+ - 变 - ，将 - - 变 +

:paramarg:

:return:

'''

ifre.findall("\+-",arg):

arg = arg.replace("+-","-")

returnadd_sub(arg)

elifre.findall("--",arg):

arg = arg.replace("--","+")

returnadd_sub(arg)

returnarg

defmul_dev_sub(arg):

'''

定义一个将"*-"和"/-"中的"-"移动到最左边，最后将"+-"和"--"整合，返回一个没有算式符号重叠的字符串

:paramarg:

:return:

'''

ifre.findall("\*-",arg):

ret1 = mul_sub.search(arg).group()

ret2 = ret1.replace(ret1,"-"+ ret1.replace("*-","*"))

arg = arg.replace(ret1,ret2)

returnmul_dev_sub(arg)

elifre.findall("/-",arg):

res1 = dev_sub.search(arg).group()

res2 = res1.replace(res1,"-"+ res1.replace("/-","/"))

arg = arg.replace(res1,res2)

returnmul_dev_sub(arg)

returnadd_sub(arg)

my_mul = re.compile("(-?\d+)(\.\d+)?(\*)(-?\d+)(\.\d+)?")#判断有乘法或者除法

my_div = re.compile("(-?\d+)(\.\d+)?(/)(-?\d+)(\.\d+)?")#判断有乘法或者除法

my_add = re.compile("(-?\d+)(\.\d+)?(\+)(-?\d+)(\.\d+)?")#判断有两个数之间加减

my_sub = re.compile("(-?\d+)(\.\d+)?(-)(-?\d+)(\.\d+)?")#判断有两个数之间加减

deftwo_count(arg):

'''

定义一个只有数字a和数字b的加减乘除算法，返回单个计算结果

:paramarg:

:return:

'''

iflen(my_mul.findall(arg)) !=:

left_num =float(arg[:(arg.index(re.search("\*",arg).group()))])

right_num =float(arg[(arg.index(re.search("\*",arg).group())+1):])

returnstr(left_num*right_num)

eliflen(my_div.findall(arg)) !=:

left_num =float(arg[:(arg.index(re.search("/",arg).group()))])

right_num =float(arg[(arg.index(re.search("/",arg).group())+1):])

returnstr(left_num/right_num)

eliflen(my_add.findall(arg)) !=:

left_num =float(arg[:(arg.index(re.search("\+",arg).group()))])

right_num =float(arg[(arg.index(re.search("\+",arg).group())+1):])

returnstr(left_num+right_num)

eliflen(my_sub.findall(arg)) !=:

ifarg[] =="-":

arg = arg[1:]

left_num =float(arg[:(arg.index(re.search("-",arg).group()))])

right_num =float(arg[(arg.index(re.search("-",arg).group())+1):])

returnstr(-left_num-right_num)

else:

left_num =float(arg[:(arg.index(re.search("-",arg).group()))])

right_num =float(arg[(arg.index(re.search("-",arg).group())+1):])

returnstr(left_num-right_num)

mul_div = re.compile("(-?\d+)(\.\d+)?(/|\*)(-?\d+)(\.\d+)?")#判断有乘法或者除法

add_sub_re = re.compile("(-?\d+)(\.\d+)?(-|\+)(-?\d+)(\.\d+)?")#判断有两个数之间加减

defsingle_count(arg):

'''

单一字符串，包含加减乘除，返回单一字符串运行结果

:paramarg:

:return:

'''

iflen(mul_div.findall(arg)) !=:

ret1 = two_count(mul_div.search(arg).group())

arg = arg.replace(mul_div.search(arg).group(),ret1)

returnsingle_count(arg)

eliflen(add_sub_re.findall(arg)) !=:

ret1 = two_count(add_sub_re.search(arg).group())

arg = arg.replace(add_sub_re.search(arg).group(),ret1)

returnsingle_count(arg)

returnarg

defi_count(arg):

iflen(re.findall("\(",arg)) !=:

ret1 = bracket.search(arg).group()

ret2 = single_count(ret1[1:(len(ret1)-1)])

arg = arg.replace(ret1,ret2)

arg = mul_dev_sub(arg)

returni_count(arg)

eliflen(re.findall("\(",arg)) ==:

arg = single_count(arg)

returnarg