String to Integer Atoi

class Solution(object):
    def myAtoi(self, s):
        """
        :type s: str
        :rtype: int
        """
        res="0"
        i = 0
        spaceflag = True
        hyphenflag = True
        while True:
            if i == len(s):
                if res=='-' or res=='+':
                    return 0
                if int(res)<-2147483648:
                    return -2147483648
                if int(res)>2147483647:
                    return 2147483647
                return int(res) if len(res)>0 else 0
            if self.isSpace(s[i], spaceflag):
                i+=1
                continue
            if self.isHyphen(s[i], hyphenflag):
                res = s[i]
                i+=1
                hyphenflag = False
                spaceflag = False
                continue
            if self.isDigit(s[i]):
                hyphenflag = False
                spaceflag = False
                res = res+s[i]
                i+=1
                continue
            if res=='-' or res=='+':
                return 0
            if int(res)<-2147483648:
                return -2147483648
            if int(res)>2147483647:
                return 2147483647
            return int(res) if len(res)>0 else 0
        
        
        
    def isSpace(self, s, flag):
        return (True and flag) if s==' ' else False
    
    def isDigit(self, s):
        return True if s=='0' or s=='1' or s=='2' or s=='3' or s=='4' or s=='5' or s=='6' or s=='7' or s=='8' or s=='9' else False
    
    def isHyphen(self, s, flag):
        return True and flag if s=='-' or s=='+' else False