If this was put into beta today in Python, it would probably get a 6kyu rating...

it's not nice, it's a cheat. Using this can lead to bannishment of the account.

Perhaps the coding is not that extreme, but it really puts your logical thinking and problem solving skills to the test. It deserves 4 Kyu

I found the sorting part trickier compared to what one would expect from a 5 or 6 kyu kata.

I mean, maybe they are afraid that their messages will get intercepted and decoded so they want to throw some invalid ones out there.

To people who already know the key they will be obvious gibberish.To people intercepting them they would get garbish that they spend hours trying to decode and are like WTF is this not decoding and it will throw all their algorithams off because they think they are valid.

well you can just try yourself to make a solution without numpy and without the determinat() method.
Took me a week, but i enjoyed it.
I´m still trying to make my own code for permutations ;)

I haven't read almost any books on Lambda Calculus, my learning was mostly from onlines sources or just practicing here. The one book I did read which was somewhat related (and very good) was To Mock a Mockingbird. Besides that, another resource you might find valuable is a very good presentation about LC. In fact, the presenter of that talk is actually a member of the Codewars community here and solves quite a few LC challenges.

By the way, if you didn't know, we've made a full esoteric style language out of LC, you should have a try of it. Example kata.

I actually agree with you. Having to check the validity of the data is frustrating and isn't the point of the kata.

I have removed all test cases sending invalid data in both this kata, and the Card-Chameleon one.

Sorry that you didn't pass on your first attempt!

I'm glad you enjoyed the kata :-)

Nothing's wrong with Python tests. I have a solution (probably not optimal) that passes all the tests in ~6 seconds. There are 5000 random tests, it would be too heavy to print something each time a test is passed. So if you time out without failing any test, you get time out. It's the same in many katas.