题解 | #二分查找-II# Python 想问一个问题

class Solution:
    def search(self , nums , target ):
        # write code here
        begin = 0
        end = len(nums) - 1
        while begin <= end:
            if target == nums[(begin + end)//2]:
                index = (begin + end)//2
#                 while target == nums[index -1] and index > 0:
                while index > 0 and target == nums[index -1]:
                        index -= 1
                return index
            elif target > nums[(begin + end)//2]:
                begin = (begin + end)//2 + 1
            else:
                end = (begin + end)//2 - 1
        return -1

假设用例是[1,1,1],1
第10行代码index = 1,进入循环,依旧满足target = nums[0],此时经过第11行index = 0,不再满足index>0.
但是用第9行测试不应该是在验证target == nums[-1],此时不应该报out of range的错误吗,但是没有,想问下是为什么？
求大佬解答,谢谢.