python 实现简单的数字字符串四则运算

#!/usr/bin/python
#  -*- coding: utf-8 -*-

import  re

# sexp = "512+((112+212)*2-312)"
# 主函数入口
def myCalculate(mystr):
    if(mystr.__contains__("(")):
        start = mystr.rindex("(")
        lstr=mystr[0:start]
        tmpstr=mystr[start+1:]
        end = tmpstr.index(")")
        rstr=tmpstr[end+1:]
        nowstr=tmpstr[0:end]
        newstr =lstr+str(myCalculate(nowstr))+rstr
        return myCalculate(newstr)
    else:
        return calcNoSym(mystr)



def calcNoSym(string):
    if(string.__contains__("*")):
        string=getNewStr(string,"*")
        return calcNoSym(string)
    if(string.__contains__("/")):
        string=getNewStr(string,"/")
        return calcNoSym(string)
    if(string.__contains__("+")):
        string=getNewStr(string,"+")
        return calcNoSym(string)
    if(string.__contains__("-")):
        string=getNewStr(string,"-")
        return calcNoSym(string)
    return string


def getNewStr(string,op):
        start = string.index(op)
        lstr=string[0:start]
        rstr=string[start+1:]
        lnum =re.search('\d+$',lstr).group()
        rnum =re.search('\d+',rstr).group()
        newstr = lstr.rstrip(lnum)+str(calcs(lnum,rnum,op))+rstr.lstrip(rnum)
        return newstr

def calcs(num1, num2,op):
    if(op=="+"):
        return int(num1)+int(num2)
    elif(op=="-"):
         return int(num1)-int(num2)
    elif(op=="*"):
         return int(num1)*int(num2)
    elif(op=="/"):
         return int(num1)/int(num2)
    else:
        raise "error"

string="11*22*3/4"

print(myCalculate(string))
sexp = "512+((112+212)*2-312)"
print(myCalculate(sexp))