leetcode String to Integer (atoi) python

class Solution(object):
    def myAtoi(self, str):
        """
        :type str: str
        :rtype: int
        """
        intMax=2147483647
        intMin=-2147483648
        str=str.strip()
        strLen = len(str)
        if strLen <= 0:
            return 0

        bolNegative = False
        tmp = str[0]
        start=0

        if tmp == '-' or tmp == '+':
            start=1

        if tmp == '-':
            bolNegative = True
        rs=0
        for i in range(start, strLen ):
            tmp = str[i]
            if tmp >= '' and tmp <= '':
                rs=rs*10+int(tmp)
            elif tmp == '-' or tmp == '+':
                return 0
            else:
                break
        intTmp = rs
        if bolNegative:
            intTmp*=-1
        if intTmp > intMax:
            return intMax
        if intTmp < intMin:
            return intMin
        return intTmp