leetcode first bad version python

# The isBadVersion API is already defined for you.
# @param version, an integer
# @return a bool
# def isBadVersion(version):

class Solution(object):
    def firstBadVersion(self, n):
        """
        :type n: int
        :rtype: int
        """
        if n < 1:
            return -1
        left=1
        right=n
        while left + 1 < right:
            mid=(left+right)/2
            bolBad = isBadVersion(mid)
            if bolBad:
                right=mid
            else:
                left=mid
        if isBadVersion(left):
            return left
        elif isBadVersion(right):
            return right
        return -1