I think it is just O(n)?? If I can assume that the functions always do simple additions and multiplications meaning they are O(1), then the function chainer will execute n of these.

So it should just be O(n), regardless of the recursive nature of this kata.

But this is not meeting the Empty string condition of returning '0'

Your solution passes all tests (sample test and full test suite).

The test case failed but the submit cases passed.

I can't remember where i've picked this up. All i know is that it works!

Thanks regardless and now I have some reading to do, lol.

Note: Pyhthon 3.8 and above

I have seen a lot of python and I have never seen this, an array assigned and used in a single line.. that would generally give you an error. Playing with it, for an unrelated example "a, b = (a := 2*5), a+10" is tremendously cool. Thank you very much sir!

It's called typing, or type annotation; read more about it here:
https://docs.python.org/3/library/typing.html

It's not enforced, and AFAIK not much used in Python, but it's used in other languages.

Your solution is great! Rather, I was hoping someone could tell me what the name of this syntax is, and what it means?

def mirror(data: list) -> list:

Why is the parameter defined like that, and what does it do?

this should help some

For some reason I did not think of this. I feel humbled.