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

why reverse_evens function is wrong

Hi, I don't understand why this is wrong. Thanks in advance. Last challenge.

def first_4(item):
    return item[:4]

def first_and_last_4(item):
    return item[:4] + item[-4::]

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

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

1 Answer

Steven Parker
Steven Parker
215,939 Points

You're half right. Your method will work when the list has an odd number of items. But when the list has an even number of items, it will return reverse odds instead.

To always return reverse evens, there's two basic strategies:

  • compute the starting position based on the list size
  • extract the even index values first, then reverse them

Either one will pass the challenge when implemented correctly.