I don’t get it!

Question

arr = [0,1,2,3,4,5,6]
i=0
for _ in arr:
del arr[i]
i = i +1
print(arr)

Output: [1,3,5]

Shouldn’t this code have deleted every element from the list????

Answer 1

jigoku_tenshi , everytime you delete an element in the list the element next to it comes to that index but the iterator does not change that's why alternate elements gets deleted

Answer 2

jigoky_tenshi , as others have also discussed, everytime you move an element from an iterator, the next element takes it's place. Instead, you should try to do this,

for i in arr:
arr.remove(i)

Answer 3

①i=0
arr[0] (=0) is deleted.
→arr[0] is changed into 1.
(arr = [1,2,3,4,5,6])
→i=1
(※"new arr[0] (=1)" has't been deleted)

②i=1
arr[1] (=2) is deleted.
→arr[1] is changed into 3.
(arr = [1,3,4,5,6])
→i=2
(※"new arr[1] (=3)" has't been deleted)

②i=2
arr[2] (=4) is deleted.
→arr[2] is changed into 5.
(arr = [1,3,5,6])
→i=3
(※"new arr[2] (=5)" has't been deleted)

③i=3
arr[3] (=6) is deleted.
(arr = [1,3,5])
→i=4

Now, cursor reached the end of array. Loop finished.

So, you have the output,
"arr = [1,3,5]".

Answer 4

Love the explanations! Thanks everyone!