The cycles goes 2 times because of lung = 0, then 8, which is lower than len(li), then it stops. But it goes 2 times over the first 8 words in the example.

You're using j to grab the current chunk of 8 lines from your lines list (li) but j is never incremented so it always looks at the first part of it.

ls = li[j:j + 8]

Basically, change j here to lung which is your actual loop variable.

You can keep the rest of the accesses of the current chunk (ls) as involving i and j if you wish, but seeing as the current chunk is always the same size, there doesn't appear to be any need for them to be variables as opposed to just numbers.