Why list comprehension skip list's element?

Question

Today get the interesting result when creating a new solution for the task by list comprehension.

def checkio(array: list) -> int:
 if array:
    return sum([x for x in array if array.index(x) % 2 == 0]) * array[-1]
 else: 
    return 0

assert checkio([0, 1, 2, 3, 4, 5]) == 30, "(0+2+4)*5=30"
assert checkio([1, 3, 5]) == 30, "(1+5)*5=30"
assert checkio([6]) == 36, "(6)*6=36"
assert checkio([]) == 0, "An empty array = 0"
assert checkio([-37,-36,-19,-99,29,20,3,-7,-64,84,36,62,26,-76,55,-24,84,49,-65,41]) == 1968

When I decided to do debugging I have seen that the sixteenth element was skipped. Why? On the Internet, I didn't find describe this cause.

Which sixteenth element was skipped? You mean -24? Why do you think it was skipped? — mkrieger1, Apr 24 '22 at 21:20

score 0 · Answer 1 · answered Apr 24 '22 at 21:25

0

array.index(x) will return the index of the first occurrence of that value, thus if you have duplicates in the array that would not work. You can look at this answer, you could achieve what you want with a list slicing:


arr = [-37,-36,-19,-99,29,20,3,-7,-64,84,36,62,26,-76,55,-24,84,49,-65,41]
print(arr[::2])

Out:
[-37, -19, 29, 3, -64, 36, 26, 55, 84, -65]

answered Apr 24 '22 at 21:25

Yolao_21

765
1
4
10

1

In this case - it's 84 at positions 9 and 16... – Jon Clements Apr 24 '22 at 21:37

Why list comprehension skip list's element?

1 Answers1