Index out of range while accessing index of the next iteration in loop in python

There are several image files in a directory on which I need to iterate through, where need to access the next iteration value in the current iteration.

img_files_list = os.listdir(/path/to/directory)
new_list =
for index, img in enumerate(img_files_list):
if img in new_list:
continue
new_list.extend([img, img_files_list[index + 1], img_files_list[index + 2]])
print(img)
print(img_files_list[index + 1])
print(img_files_list[index + 2])


I need to iterate over all the items of the img_files_list but when reached at the end of the loop need to properly come out of loop without index out of range exception. Anyone, please point out where do I missed the logic.

index + 1

index + 2

img_files_list[10]

img_files_list[11]

2 Answers
2

Seems more like Code Review than Stack Overflow.

When you reach the last item in your for image, img in enumerate(img_files_list) line, there is no item after the last one. This is what causes an IndexOutOfRangeException.

for image, img in enumerate(img_files_list)

IndexOutOfRangeException

There are a few ways to approach this:

As Sruthi V. wrote, include a condition:

print(img_files_list[i])
if i + 1 < len(img_files_list):
print(img_files_list[i + 1])
if i + 2 < len(img_files_list):
print(img_files_list[i + 2])


Include a try... except:

try... except

try:
print(img_files_list[i])
print(img_files_list[i + 1])
print(img_files_list[i + 2])
except IndexOutOfRangeException:
pass


Limit the range of your loop:

i_img = list(enumerate(['a', 'b', 'c', 'd', 'e']))
for i, img in i_img [:len(i_img ) - 2]:
print(img)
print(i_img[i + 1])
print(i_img[i + 2])


Note that you have no reason to use enumerate — you're just using it to get indices. You also don't need your if img in new_list — you're just using it to skip the next two. You can make this more elegant and solve your problem using range (a modified solution 3).

enumerate

if img in new_list

imgs = os.listdir('/path/to/directory')
triplets =
for i in range(0, len(imgs) - 2, 3):
triplet = [imgs[i], imgs[i + 1], imgs[i + 2]]
triplets.extend(triplet)
print('n'.join(triplet))


N.B. I'm not sure what you're even trying to do. Even your if img in new_list might be a mistake since it just skips the last 1-2 final items. And if that were gone, all you would be doing is making a copy of this list and printing its contents. In which case I would suggest:

if img in new_list

imgs = os.listdir('/path/to/directory')
print('n'.join(imgs))


But if you clarify what you're trying to do, I can edit this answer.

From my comment to your question:

index + 1 and index + 2 cause a problem for last 2 items. For
example, if your list's size is 10, then indexes will be 0,2,...,9.
When the index is 8 and 9, you are trying to execute
img_files_list[10] and img_files_list[11]. So the index is out of
range.

index + 1

index + 2

img_files_list[10]

img_files_list[11]

I assume that you want to access images as 3-item list, then I suggest you a little bit different way. I will use an integer array instead of images for a better understanding.

img_files_list = [0,1,2,3,4,5,6,7,8,9]
new_list =
n = 3
for i in range(0, len(img_files_list), n): # Respectively, i is 0,3,6,9,...
temp = img_files_list[i:i+n]
print(temp)
new_list.extend(temp)


Output:

[0, 1, 2]
[3, 4, 5]
[6, 7, 8]
[9]


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