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Python Python Collections (2016, retired 2019) Slices Slice Functions

Posted by Cristian Glodeanu
Cristian Glodeanu
4,031 Points

Task 4 of the Code Challenge is... picky?

Hi,

For the last task, 4 of 4, the auto-grader won't accept this solution:

def reverse_evens(iter_item):
    return iter_item[-1::-2]

However, running this locally works:

>>> a = list(range(1,6))                                                                                  
>>> a                                                                                                     
[1, 2, 3, 4, 5]                                                                                           
>>> a[-1::-2]                                                                                             
[5, 3, 1]

Any of you ran into this as well? Thanks!

1 Answer

Alexander Davison
Alexander Davison
65,469 Points

Your code sort of works, but it only works for lists that have an odd length.

If the length of the list is even, you should doiter_item[0::-2]. However, as I said, that snippet only works for lists length even.

So, you would probably have to use an if/else statement to test if the length of the list is even or odd :smile:

Here's a hint:

To test if a number is even, you can do this:

Pretend I'm in the Shell

>>> a = 10
>>> a % 2 == 0  # This tests "is a even?", and it is so Python returns True
True
>>> b = a - 1  # In this case, b will be 9 (which is a - 1)
>>> b % 2 == 0
False

If you have questions on the % operator, respond below with the text #modoperator inside and I'll explain. :)

I hope this helps :grin:

Happy coding! :tada:

:dizzy: ~Alex :dizzy: