that is a smart solve ,, i like it , i know that is don't best practice and there was more solutions is more readable than it's but this is a new practice and a new way for the solution for me, so i like it.
i know my english language is bad :)

Idiomatic in PL means "as intended by language authors", "according to idioms on which the language was designed". And because language authors usually know better how the language should work, idiomatic is good.

What does "idiomatic" mean? And why is it a good thing?

I found it just by looking at first elements of each row. Saw that they are close to n squared, but not quite.

did not know that, cool! thx

list() isn't actually needed, join can iterate through a string.

how did he find the relation!!

I think this solution is harder to read than an inline if

Writing a function to do the work of a builtin isn't very idiomatic though either.

shortest, but not idiomatic

This will not ignore the case sensitive.