我应该在try-except块中添加else语句来处理return语句吗？

Question

I am trying to compare items in a list and find any locations where an item may be missing.

I am using a for loop by enumerating the list to compare the number within the current item with the next item and check that the number within the next item is only larger by 1. It seems to me that I should use a try-except block so that I don't receive an IndexError when the last iteration of the loop is ran and tries to compare to the next item that doesn't exist.

file_list = []
for i in range(100):
    file_list.append('img' + str(i).zfill(3) + '.tif')

del file_list[50]

for i, file in enumerate(file_list):
    try:
        if int(file[3:6]) + 1 != int(file_list[i + 1][3:6]):
            return 'File missing after {}'.format(file_list[i])
    except IndexError:
        print('IndexError at i = {}'.format(i))

This code works, however I have read that you should try to avoid placing much code in the try block itself to avoid adding code that could raise exceptions from other locations than the portion of the code that is intended to be tested. In this case, should I add an else statement in the try-except block to place the return statement? How do I manage the if statement in that case?

Answer 1

It seems to me that I should use a try-except block so that I don't receive an IndexError when the last iteration of the loop is ran and tries to compare to the next item that doesn't exist.

I think a better solution is to write code that doesn't raise exceptions under normal conditions.

Instead of comparing the current item to the next item, which as you noted will cause an exception on the last item, you can iterate starting on the second item and compare to the previous item:

for i in range(1, len(file_list)):
    # compare file_list[i] to file_list[i-1]