How do I use the sum() function in Python to find the sum of all positive numbers in a list?

Question

Edit 1: Solved! The solution was using i for i in arr if i > 0, which was given to me by @sushanth.

Final product of the code:

def positive_sum(arr):
    return sum(i for i in arr if i > 0)

I am trying to complete some Codewars challenges, and I came across one that is giving me issues. I am given a list of positive and negative numbers, and I am supposed to find the sum of all of the positive numbers.

Here is what I already have:

def positive_sum(arr):
    for n in arr:
        if n < 0:
            arr.remove(n)
    return sum(arr)

Here are the lists I am supposed to be working on:

[1,2,3,4,5]
[1,-2,3,4,5]
[-1,2,3,4,-5]
[]      
[-1,-2,-3,-4,-5]

However, whenever I run the tests, all of the tests pass except for the last one, with all of the negative numbers. For some reason, the result of it is -6, even though all negative numbers should have been removed.

Why is this? What should I do to make sure all of the tests pass?

instead of remove, you can use ``sum(i for i in arr if i > 0)`` ? — sushanth, Mar 09 '21 at 17:43
Don't remove from a list while iterating it. You're messing with the iterator which can lead to elements being skipped. — Carcigenicate, Mar 09 '21 at 17:44
@sushanth yep, that worked! I did something similar to this from another stackoverflow post, but I think it was meant to be used in another use case. This one worked perfectly! — LiterallyJohnny, Mar 09 '21 at 17:46
Does this answer your question? [How to remove items from a list while iterating?](https://stackoverflow.com/questions/1207406/how-to-remove-items-from-a-list-while-iterating) — Random Davis, Mar 09 '21 at 17:47

Vova · Answer 1 · 2021-03-09T17:55:25.510

2

try sum() with generator and if condition:

result = sum(x for x in [1, 2, 3, 4, 5] if x > 0)
print(result)

edited Mar 09 '21 at 17:55

answered Mar 09 '21 at 17:48

Vova

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No need to use a `list` comprehension, `sum()` can take a generator as an argument. Creating a `list` first wastes memory and computation time. – ddejohn Mar 09 '21 at 17:51
Although, play around with it. Generator expressions also tend to be slower, so for small lists, a comprehension may be the better option if the extra memory usage is acceptable. – Carcigenicate Mar 09 '21 at 17:54
entirely agreed, changed to generator, good catch, thanks! – Vova Mar 09 '21 at 17:56

How do I use the sum() function in Python to find the sum of all positive numbers in a list?

1 Answers1