I consider this clever and readable, not best practice because it technically goes over the list twice, which can be done with one pass in exchange for less readability. Not much overall difference though. Good job.

just four lines

I learned a new way to keep count of a value occurring in an iterator. Thanks!

At this point, I'm beginning my journey in efficient coding and comments like this have helped me to understand time/space complexity and learning algorithms

Why are you iterating over array twice? it seems wastefull

beautiful

yeah, probably

isnt replacing len(arr) with arr better

Doesn't work for None

really enjoying this solution.

It doesn't seem to work properly if the function argument is None, count_positives_sum_negatives(None).

the 1 in front of the for turns the temporary variable into a 1. That's necessary because you want to count one by one and not add the content of the array.

it is necessary otherwise for empty list it will return [0,0] rather than []

Well, both bool([]) and len([]) returns False. "if arr" is a more pythonic way than "if len(arr)"

the len() is unnecessary, and looping through twice is unnecessary