Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Python

Posted by Justo Montoya
Justo Montoya
3,799 Points

backwards, 3rd sorting of a list

in the sorting slices coding challenge I'm having trouble with the third part of the challenge whereby you have to: "create a variable named silly_list that is every third item, backwards, from messy_list. For example, the first two items in silly_list should be [-1, 8]."

messy_list = [5, 2, 1, 3, 4, 7, 8, 0, 9, -1]
clean_list=messy_list[:]
clean_list.sort()
silly_list=messy_list[9:0:-3]

I'm having trouble with the fourth line particularly. It prints ====>[-1,8,3] I'm not sure why it isn't printing 5 as well.

I tried 

silly_list=messy_list[len(messy_list):0:-3]

as well but it still won't pass the challenge.

To my understanding, I have the indices and skipping correct so I'm not sure why it's not working.

Nathan Tallack
Nathan Tallack
22,164 Points
Nathan Tallack
Nathan Tallack
22,164 Points

Could you link to the challenge for us?

1 Answer

Haider Ali
.a{fill-rule:evenodd;}techdegree seal-36
Haider Ali
Python Development Techdegree Graduate 24,728 Points

Hi, I have taken a look at your code and seen that you are over complicating your code by a lot. The solution is as simple as this:

silly_list = messy_list[::-3]

The -3 shows that we are starting at the end of the list and that we are going back three steps each time. So, in this case we are saying go from the end to the beginning and -3 every time.

I hope that my explanation was clear and that I managed to help you.