[Leetcode][python]String to Integer (atoi)/字符串转整数 (atoi)

class Solution(object):
    def myAtoi(self, str):
        """
        :type str: str
        :rtype: int
        """
        INT_MAX =  2147483647
        INT_MIN = -2147483648
        result = 0

        if not str:  # 不是str返回0
            return result

        i = 0
        while i < len(str) and str[i].isspace():  # 判断空格
            i += 1

        sign = 1  # 若有‘-’结果相反数
        if str[i] == "+":
            i += 1
        elif str[i] == "-":
            sign = -1
            i += 1

        while i < len(str) and str[i] >= '0' and str[i] <= '9':
            if result > (INT_MAX - (ord(str[i]) - ord('0'))) / 10:
                return INT_MAX if sign > 0 else INT_MIN
            result = result * 10 + ord(str[i]) - ord('0')
            i += 1

        return sign * result