leetcode python

# Implement atoi to convert a string to an integer.## Hint: Carefully consider all possible input cases.# If you want a challenge, please do not see below and ask yourself what are the possible input cases.## Notes: It is intended for this problem to be specified vaguely (ie, no given input specs).# You are responsible to gather all the input requirements up front.## Update (2015-02-10):# The signature of the C++ function had been updated.# If you still see your function signature accepts a const char * argument,# please click the reload button  to reset your code definition.class Solution(object):    def myAtoi(self, str):        """        :type str: str        :rtype: int        """        i = 0        sign = 1        base = 0        l = len(str)        INT_MAX = 2147483647        INT_MIN = -2147483648        a_0 = ord('0')        a_9 = ord('9')        while i < l and str[i] == ' ':            i += 1        if i < l and str[i] == '-':            sign = -1            i += 1        elif i< l and str[i] == '+':            i += 1        while i < l and ord(str[i]) >= a_0 and ord(str[i]) <= a_9:            if base > INT_MAX / 10 or (base == INT_MAX / 10 and ord(str[i]) - a_0 > 7):                return sign == 1 and INT_MAX or INT_MIN            base = 10 * base + (ord(str[i]) - a_0)            i += 1        return base * sign