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

Posted by Jaeeun Lee
Jaeeun Lee
Courses Plus Student 1,246 Points

Reverse Slice

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

When I enter `reverse_evens([1,2,3,4,5]) in my console, it returns [5, 3, 1], which is what the task asks for. However, the challenge keeps says it does not return the correct value. Why would that be?

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

def first_and_last_4 (iterable):
    return iterable[:4] + iterable[-4:]

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

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

5 Answers

Ben Reynolds
Ben Reynolds
35,170 Points
Ben Reynolds
Ben Reynolds
35,170 Points

This one's pretty hard, I'll give you a few hints to get started.

The index you start counting from will be different depending on whether and even or odd number of items was passed in. So I started by setting a variable to get the length of "iterable" and named it "length."

I used an if/else to check if length was even or odd and have two different versions of the return statement. The return statement you're using will work for 1, 2, 3, 4, 5 (odd number of items), but wouldn't work for 1, 2, 3, 4, 5, 6.

mauricio almonte
mauricio almonte
1,913 Points

did you see this one? I'm doing exactly what you said, and no luck! im trying this on my own environment and is working! 

def first_4(papa):
    return papa[0:4]
def first_and_last_4(popo):
    return popo[:4] + popo[-4:]
def odds(pipi):
    return pipi[1::2]
def reverse_evens(pepe):
    nana = len(pepe) -1
    if int(nana /2) * 2 == len (pepe) - 1:
        return pepe[-1::-2]
Jaeeun Lee
PLUS
Jaeeun Lee
Courses Plus Student 1,246 Points
Jaeeun Lee
Jaeeun Lee
Courses Plus Student 1,246 Points

I think I misunderstood the question. I thought it was asking for even index numbers from the reversed list, not from the original list.

mauricio almonte
mauricio almonte
1,913 Points
mauricio almonte
mauricio almonte
1,913 Points

i did this and not even like this i got it to work, i don't understand where I'm failing. 

def first_4(papa):
    return papa[0:4]
def first_and_last_4(popo):
    return popo[:4] + popo[-4:]
def odds(pipi):
    return pipi[1::2]
def reverse_evens(pepe):
    nana = len(pepe) -1
    if int(nana /2) * 2 == len (pepe) - 1:
        return pepe[-1::-2]
Ben Reynolds
Ben Reynolds
35,170 Points
Ben Reynolds
Ben Reynolds
35,170 Points

The logic for my approach would look like this:

def reverse_evens (iterable):
    length = len(iterable)
    #if length is even:
        #return one version of the slice
    else:
        #return another version of the slice
mauricio almonte
mauricio almonte
1,913 Points

God Damwit!!! now i see it, my version only applies to only one scenario. i was like "naaaa they dont need the ELSE: statement"

Marzoog AlGhazwi
Marzoog AlGhazwi
15,796 Points
Marzoog AlGhazwi
Marzoog AlGhazwi
15,796 Points

can't find what is wrong with mu code

def first_4(iterable):
    return iterable[:4]

def first_and_last_4(iterable):
    return iterable[:4] + iterable[-4:]

def odds(iterable):
    if len(iterable)%2 == 0:
        return iterable[-2::-2]
    else:
        return iterable[-1::-2]
mauricio almonte
mauricio almonte
1,913 Points

@Marzoog Al Ghazwi you are doing the last challenge, not the 3rd one, your "odds" funtion content is from the last challenge the one that is called "reverse_evens", so you are either missing the third challenge or you need to change the name of the funtion that is being expected