class Solution:

    def StrToInt(self, s):

        res,pos,mult = 0,1,1 ###res是初始返回值；pos是正负标记；mult是位数的乘数，个位是1，十位是10，百位是100

        if not s:#字符串为空

            return res

        elif len(s)==1:#字符串长度为1单独讨论

            if 48 < ord(s) <= 57:

                return ord(s)-48

            else:

                return 0

        elif s[0]=='-' or s[0]=='+':#字符串前面有正负号单独讨论

            if s[0]=='-' and s[1]!='':

                pos = -1

                s = s[1:]

            elif s[0]=='-' and s[1]=='':

                return res

            elif s[0] =='+' and s[1]!='':

                pos = 1

                s = s[1:]

            elif s[0]=='+' and s[1]=='':

                return res

        for i in range(len(s)-1,-1,-1):#对去掉正负号的字符串依次取值

            if '' >= s[i] >= '':

                res += (ord(s[i])-48)*mult

                mult = mult*10

            else:

                 return 0

        return res*pos