That's a twoliner though.

wow made a functionnal oneliner that actually is pythonic... yay

Elegant. Congrats.

A lot of people think that this kata is easy. Maybe it is, if you have a CS bacground. I tried solving this 3 months ago and got stuck. That's only recently that I read about the stack data structure and the solution pricked up in my mind. I think 4ku is the right level for this kata.

He's making sure that count[a] is a number. You can think of it as a shortcut to Number(count[a]).

You know what, that's actually a good point. In some cases you can be reasonably confident that the method you're writing will only concatenate a small number of strings or will not be run a huge number of times, so the difference in performance is going to be insignificant.

I should probably have phrased my initial response differently, along the lines of "yo, concatenating is ok in small doses, but .join() is a lot faster if you are gonna do that with a lot of strings; it also makes you look good on job interviews". Unfortunately, don't think I can edit it.

Cheers :)

Yes, string addition is slower than joining a list. But it's only significant if you are adding a lot of strings together.
Here's a nice article about this problem when the number of strings to be added are small The Sad Tragedy of Micro-Optimization Theater

When adding 2 or 3 strings together, it has no performance overhead whatsover compared to making a list and joining it.
And since this method is much more clear and pythonic, it is best practice.

Unfortunately this is NOT a 'best practice'. String concatenation using + operator is some 30 times slower than using "separator".join(iterator_to_be_joined).

For additional reading: https://waymoot.org/home/python_string/

Thank you.

Congrats man, elegant code.