This solution was definitely easier to understand. Smart to put the rows variable inside the loop so it resets every time to add it to the columns variable. Saves lots of space and makes it a lot more clean and concise.

I am wondering if matrix is a better name here instead of columns?

I agree the only positive side to list comprehension is just how consise it is and the speed of execution (it runs faster than traditional nested loops).

compr may be faster but loops are easier to understand

Hello, nicely solved. can you please explain how this works, and specially how and why you are using index here?

No: https://stackoverflow.com/questions/30245397/why-is-a-list-comprehension-so-much-faster-than-appending-to-a-list