如何使用列表切片来完成此操作？

Question

SUMMER OF '69: Return the sum of the numbers in the array, except ignore sections of numbers starting with a 6 and extending to the next 9 (every 6 will be followed by at least one 9). Return 0 for no numbers.

    summer_69([1, 3, 5]) --> 9
    summer_69([4, 5, 6, 7, 8, 9]) --> 9 
    summer_69([2, 1, 6, 9, 11]) --> 14

This is the problem. I have been trying to solve this using list slicing but have been unable to. Note: 9 can only be trailing 6, not before 6.

Here's what my logic is- I found out the index of 6 and assigned it to a variable and I found the variable of 9 and assigned a variable to it too. The other two conditions are satisfied but the condition with 9 doesn't get satisfied no matter what I try.

Here is some code from my side. Please excuse my bad programming skills.

def summer_69(arr):
    if 6 not in arr:
        return sum(arr)
    elif 6 and 9 in arr:
        i = arr.index(6)
        y = arr.index(9)
        sxy = sum(arr[i:y])
        return sum(arr) - sxy
    else:
        i = arr.index(6)
        return sum(arr[:i])

For an array [4, 5, 6, 7, 8, 9] I am getting the output 18.

Answer 1

Done without slicing.

def summer_69(l):
    sign, count = False, 0
    for num in l:
        if num == 6:
            sign = True
        if not sign:
            count += num
        if num == 9:
            sign = False
    return count

Answer 2

my solution is:

def sum67(nums):
    add = True
    sum1 =0
    for i in range(len(nums)):
        if add:
            if nums[i] == 6:
                add = False
            else:
                sum1 += nums[i]
        else:
            if nums[i] == 7:
                add= True
    return sum1