I am really not sure about this. Inputs go slightly above 1M, and determining whether a number of magniture 1M is prime is not that expensive, or difficult. Some optimization techniques are to be expected for a 5 kyu kata, but this kata requires only very basic ones, nothing really fancy.

how on earth is this an issue

The optimisation requirement feels steep, especially for a 5 kyu problem.
My code completes a test case in ~0.5s with a relatively efficient solution.

More readable than the other "one-liner" solutions (I know it's multiple lines but it's one statement, ykwim)

I have to wonder though... ' ' * 3 is more effort to type that ' ' lol, what's the deal with that?

+1

lmao

Eh, agree to disagree. Wouldn't call it "hacky", it's just not very neat. I'd personally find it easier to read a multiline solution

I've seen hacky code before - this isn't hacky in the least. If anything, it's the most idiomatic way to do this, imo.

Who voted best practises lmao? If I saw this in a codebase I'd cry

Still, outside of production, I love clever one liners - +1.

so clean !

Turing would be proud