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

Posted by Patrick Tse
Patrick Tse
10,682 Points

Couldn't get pass Challenge Task 4 of 4. (reverse_evens)

def reverse_evens(iterable_item): return iterable_item[::-2]

print(reverse_evens([1,2,3,4,5]))

[5,3,1] Verified it in workspace but it keeps saying its not correct. Not sure what is missing.

slices.py 
def first_4(iterable_item):
    return iterable_item[:4]

def first_and_last_4(iterable_item):
    my_list = iterable_item[:4]
    my_list.extend(iterable_item[-4:])
    return my_list

def odds(iterable_item):
    return iterable_item[1::2]

def reverse_evens(iterable_item):
    return iterable_item[::-2]
Todd Costa
Todd Costa
3,380 Points
Todd Costa
Todd Costa
3,380 Points

I'm stuck on the same exact task, i believe the issue that you're running into (which i did too) is if the list ends with an odd index number. ie lets say the last iterable_item is index 21, they want only the even indexs so your would need to disregard the very last item. Please post if you figure it out, i'm not making any headway.

2 Answers

Todd Costa
Todd Costa
3,380 Points
Todd Costa
Todd Costa
3,380 Points

Sorry for the double post but writing my response to you helped me think it through.

First get the even indexs iter = iter[::2] Then reverse it return iter[::-1]

Leon Silcott
Leon Silcott
27,584 Points
Leon Silcott
Leon Silcott
27,584 Points

For anyone's future reference, I solved this by using doing the following:

def reverse_evens(given):
    #Check to see whether list is odd length or even 
    if len(given) % 2 != 0:
        # If list is odd start from the first last index and iterate -2 (will always be odd)
        given = given[-1::-2]
    else:
        # If list is even start from the second to last index (now odd index) and iterate -2
        given = given[-2::-2]
    # Return the newly generated given list
    return given

Hope it helps!