Yep, i also tried it with javascript, with the same result (timed out)

On my local laptop, python for 10^9 string runs at about 4ms, so it should be ok time-wise.
However, when i tried to generate a random 10^9 string on my laptop, this took a really long time.

I suspect the issue to be with system entropy pool / random number generator performance.

I also experience the same issue, both with python and with javascript

as long as nobody answered to your comment, you should be able to remove it. => Try for the one below. ;)

about your problem: I believe the kata is uncompletable for now in python because of a runner issue (edit: see the thread just below yours)

(sorry for the duplicate, couldn't see my first comment)

Execution Timed Out (12000 ms)

My solution code:

def triangle(row):
  return ''