这题还真是奇葩啊

class Solution:
    # @return an integer
    def atoi(self, str):
        str = str.strip()
        newStr = []
        for i in xrange(len(str)):
            if '0' <= str[i] <= '9' or (str[i] in ('+', '-') and i == 0):
                newStr.append(str[i])
            else:
                break
        if newStr in ([], ['+'], ['-']):
            return 0
        elif -2147483648 <= int(''.join(newStr)) <= 2147483647:
            return int(''.join(newStr))
        elif int(''.join(newStr)) > 2147483647:
            return 2147483647
        else:
            return -2147483648