String to integer (Leetcode 8) easy python solution

gistfile1.txt

class Solution(object):
    def myAtoi(self, s):
        """
        :type s: str
        :rtype: int
        """            

        sign = ""
        res = 0
        number_read = False
        for i in range(len(s)):
            if s[i] == '+' or s[i] == '-':
                if sign or number_read: break
                else: sign = s[i]
            
            elif s[i] >= '0' and s[i] <= '9':
                number_read = True
                res *= 10
                res += int(s[i])
            
            elif s[i] == ' ':
                if number_read or sign: break
            
            else: break
            
        int_max = (2 ** 31) - 1
        int_min = -2 ** 31
        if sign == '-': res *= -1
        if res > int_max: return int_max
        if res < int_min: return int_min
        return res