I think there should be a validation for wrong code input. like below

brain_luck('[,+[-.,+]', 'Codewars' + chr(255))

And this just made me, ow weee I am what people aspire to be :XD

I solved it the same way at first, but in no way is this more efficient.
At least take the n*2-1 calculation out of the list comprehension. you don't need to calculate that in every loop.

Check my solutions.