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

Posted by Oleg Bondar
Oleg Bondar
2,913 Points

reverse_evens goes bad

I'm trying to solve reverse_evens function like this but it gives me an error:

Why it happens?? I have tried this on python console and it's ok!

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

def first_and_last_4(iterable):
    r = iterable[:4]
    r.extend(iterable[-4:])
    return r

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

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

1 Answer

Steve Hunter
Steve Hunter
57,712 Points

Hi Oleg,

Do this one in two stages. Get the evens first and store that in a new list. Then, reverse it. Just using -2 is length dependent - you'll get different results depending on the length of the iterable.

So step through the evens first with [::2] and store that temporarily. Then return the reverse of that using [::-1].

Make sense?

Steve.

David Mobley
David Mobley
2,609 Points
David Mobley
David Mobley
2,609 Points

Thanks Steve, I was beating myself up with this... I feel kinda dumb because the solution was so simple... #derp