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

Antoine Solomon
Antoine Solomon
2,850 Points
Posted by Antoine Solomon
Antoine Solomon
2,850 Points

My implementation of the reverse_evens() doesn't seem to work. Could you review my function ?

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

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

def first_and_last_4(list):
    first_4 = list[:4]
    last_4 = list[-4:]
    return first_4 + last_4

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

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

4 Answers

Chris Jones
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.a{fill-rule:evenodd;}techdegree seal-36
Chris Jones
Java Web Development Techdegree Graduate 23,933 Points
Chris Jones
.a{fill-rule:evenodd;}techdegree seal-36
Chris Jones
Java Web Development Techdegree Graduate 23,933 Points

Hi Antoine,

You just need to change the -1 to a -2. Like so, [-2::-2]. I tested this in the Python shell and it worked.

Python 2.7.14 (v2.7.14:84471935ed, Sep 16 2017, 20:19:30) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> iterable = [1,2,3,4,5,6,7,8,9]
>>> iterable[-2::-2]
[8, 6, 4, 2]

However, the code challenge didn't accept it, so I tried the more verbose code below and it passed.

def reverse_evens(iterable):
    results = []
    for i in range(0, len(iterable), 2):
        results.append(iterable[i])
    return results[::-1]

Let me know if you have any questions!

Antoine Solomon
Antoine Solomon
2,850 Points
Antoine Solomon
Antoine Solomon
2,850 Points

Hi Chris,

Thanks for commenting. I was going nuts with that particular issue.

Antoine Solomon
Antoine Solomon
2,850 Points
Antoine Solomon
Antoine Solomon
2,850 Points

Looking at Chris Jones's answer I figured I could just use the list copy() method

def reverse_evens(list):
    result = list.copy()
    return result[-2::-2]
Antoine Solomon
Antoine Solomon
2,850 Points
Antoine Solomon
Antoine Solomon
2,850 Points

Actually i retested my solution and it didn't work. :-(

Chris Jones
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Chris Jones
Java Web Development Techdegree Graduate 23,933 Points
Chris Jones
.a{fill-rule:evenodd;}techdegree seal-36
Chris Jones
Java Web Development Techdegree Graduate 23,933 Points

Oops :(. It could just be me, but I felt like the Python code challenges were the most picky of the languages I've learned through Treehouse. It seemed like most were looking for you to solve the challenge a specific way, rather than verifying your end result.