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Chris Komaroff
Courses Plus Student 14,198 PointsNot passing challenge 4 of 4 - slices.py
Am I missing something? This is weird. I think I have the right answer. Easy python slice question, can someone help me? See my solution for reverse_evens(). Thanks!
def first_4(iter):
return iter[:4]
def first_and_last_4(iter):
return iter[:4] + iter[-4:]
def odds(iter):
return iter[1::2]
# This correct: [5,3,1]
#def reverse_evens(iter):
# return iter[-1::-2]
# This is correct: [5,3,1]
#def reverse_evens(iter):
# return iter[4::-2]
# This is correct: [5,3,1]
def reverse_evens(iter):
return iter[::-2]
5 Answers
Jason Anello
Courses Plus Student 94,610 PointsHi Chris,
The slices you have tried will only work part of the time. They would either work on odd length iterables or even length, but not both.
You could set up some if/else condtional logic to check the length of the iterable and then do the appropriate slice.
But you could accomplish this in 1 line by doing 2 slices. The first slice would get the even indexes and a slice on that to reverse it.
Taylor Schimek
19,318 PointsHey Chris, iter[::-2] starts at -1. What if -1 isn't even?
Chris Komaroff
Courses Plus Student 14,198 Pointsiter[-2::-2] does not pass either.
Thomas Helms
16,816 PointsI see your logic, since I had the same concept as well. What threw me off was the hint of [5,3,1]. The problem is that those numbers aren't at even indexes; they are evenly spaced, sure.
Jason has the right direction: start by slicing the evens, in the normal way [::2]. Then iterate through that slice backward.
Jason Anello
Courses Plus Student 94,610 PointsThe list in the example was [1, 2, 3, 4, 5] The even indexes are 0, 2, and 4 and the numbers at those indexes are 1, 3 and 5
If you reverse the even indexes you would get [5, 3, 1]
Taylor Schimek
19,318 PointsNeed to check the length of the list that is coming in. It won't necessarily be the same as the example. Once you know the length, you can proceed accordingly, either list[::-1] or list[::-2]
Jason Anello
Courses Plus Student 94,610 PointsIt's easier to do 2 slices but if you're going to check the length then [::-1] isn't going to work. That's only going to reverse the list.
Taylor Schimek
19,318 PointsRight. My bad. Meant start at -1 or -2. I did it by checking the length.
Chris Komaroff
Courses Plus Student 14,198 PointsChris Komaroff
Courses Plus Student 14,198 PointsLast suggestion is really cool, just one line of code. Thank you.