reverse_even

Question

I need help with the code for the function reverse_evens.

It's supposed to return a slice starting from the end of the iterable, but only for every value with an even index.

I feel dumb. Please send help.

slices.py

def first_4(mylist):
    return mylist[0:4]

def first_and_last_4(mylist):
    return mylist[0:4] + mylist[-4:]

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

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

Answer 1 · 2018-01-10T04:42:33Z

January 10, 2018 4:42am

Hello!

So the meat of challenge 4 is: Return every item in the iterable with an even index...in reverse.

Given the list: [1, 2, 3, 4, 5], we want the following indexes: 0, 2, and 4. Our list would become [1, 3, 5]. Reversed, this is [5, 3, 1]. Your code works great for this example!

But what if our list is not an odd length. What if we had [1, 2, 3, 4, 5, 6] for example? We want the following indexes: 0, 2, and 4. Our list would become [1, 3, 5] then reversed to [5, 3, 1].

Here is where your code presents a problem.

>>> x = [1, 2, 3, 4, 5]
>>> y = [1, 2, 3, 4, 5, 6]

>>> x[-1::-2]
[5, 3, 1]
>>> y[-1::-2]
[6, 4, 2]

Your code starts at the last index, not at the last even index. In order to solve this, I would suggest separating it into 2 list commands (mylist[...][...]), one to get the even numbers and one to reverse the list.

I hope this helps! If you still don't understand anything, feel free to reply :)

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Koki Kira

Koki Kira

reverse_even

1 Answer

Logan R

Logan R

Koki Kira

Koki Kira