String to Integer (atoi) – Python 3 (Week 10 – 19)

 class Solution:
    def myAtoi(self, str: str) -> int:
        str = str.strip()
        
        if len(str) == 0:
            return 0
        elif str[0] != '-' and str[0] != '+' and not str[0].isdigit():
            return 0       
        ans = 0
        
        start, end = 0, 0
        isNegative = False
        if str[0] == '+':
            start += 1
            end += 1
        elif str[0] == '-':
            isNegative = True
            start += 1
            end += 1
            
        
        if start >= len(str) or not str[start].isdigit():
            return 0
        
        while end < len(str) and str[end].isdigit():
            end += 1
        
        ans = int(str[start:end])
        
        if isNegative:
            ans = -ans
        
        if ans < -2**31:
            ans = -2**31
        elif ans > 2**31 - 1:
            ans = 2**31 - 1
        
        return ans