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

Leo Marco Corpuz
Leo Marco Corpuz
18,975 Points
Posted by Leo Marco Corpuz
Leo Marco Corpuz
18,975 Points

reverse evens

Can't solve the last part of this challenge

slices.py 
def first_4(numberSet):
    return numberSet[0:4]

def first_and_last_4(numberSet):
    return numberSet[:4] + numberSet[-4:]
def odds(numberSet):
    return numberSet[1::2]
def reverse_evens(numberSet):
    return numberSet[-2::-2]

1 Answer

adamzemmoura
adamzemmoura
29,481 Points

You can break this task down into two parts.

1) Get all the numbers corresponding to even indexes. Note: it’s even indexes here so requires a step of 2 eg. Index 0, then 2, then 4 and so on. We can do this using slices by leaving the start and stop blank, which gives us the default behaviour of starting at the beginning and going all the way to end and specifying a step of 2 to get only the even indexes. 

numberSet[::2]

2) Reverse the list returned from step 1. Using slices to do this we can again leave the start and stop blank as we did in step 1 and specify -1 as the step, which means : start at the end and go through the list backwards, which is one way to reverse the order. 

numberSet[::-1]

Steps 1 and 2 can be combined on one line making your function : 

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

Hope this helps.