Thanks for the advice, i'm new on this website.
What is considered a spoiler?
I thought about it before posting it but since the solution was provided, i didn't think it could be an issue, i guess i was wrong :p

Please use a spoiler flag, comments are visible by default to everyone (I put the flag for you this time).

thx! :) (Note: do not forget the spoiler flag, when you throw bits of code in the comments: they are visible from anyone in their dashboard)

What list lengths were tested? If it's function calls that are expensive, it's still a constant factor, it may be able to significantly affect times for only really small lists.

@KenKamau: I understand. Don't get me wrong, this wasn't meant as criticism, just as a fun little observation in case other users wondered if and how the two top voted solutions differed.

@Unnammed: My comment was based on the following timeit results (first fct is sum(arr1+arr2):

array_plus_array1 took 5.588323692000131 secs to complete 10000000 repetitions
array_plus_array2 took 6.547926787000051 secs to complete 10000000 repetitions

So as you can see the performance difference is very small, but it's there. My best guess is that's caused by the additional function call which to my knowledge can be pretty expensive in Python.

Proof? I don't believe adding numbers can be slower than adding the same numbers and allocating memory for a whole list and copying everything.

It's 8 Kyu. I don't think about performance in such Katas.