leetcode-8-字符串转换整数（atoi)

class Solution:
    def myAtoi(self, str: str) -> int:
        str = str.strip()
        if str == "":
            return 0
        left = 0
        right = 0
        maxi=2147483647
        mini=-2147483648
        if str[0]=="+" or str[0]=="-":
            left = 1
        if(left==1 and len(str)==1) or str[left]<"0" or str[right]>"9":
            return 0
        for i in range(left,len(str)):
            if str[i]>=‘0‘ and str[i]<=‘9‘:
                right = i
            else:
                break
        res = str[left:right+1].lstrip("0")
        if len(res)==0:
            return 0
        else :
            res=eval(res)
        if left==1 and str[0]==‘-‘:#判断正负 
            res=-res 
        if res>maxi: 
            return maxi 
        elif res<mini: 
            return mini 
        else :
            return res