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

Martin Mõtsar
Martin Mõtsar
2,844 Points
Posted by Martin Mõtsar
Martin Mõtsar
2,844 Points

#I can't get the right outputs from the last task, even though testing in PyCharm I get the sam results as in the sample

I tried two approaches to the task, but still it doesn't work. Am I way off the the task?

slices.py 
numbrid=list(range(10))
def first_4(numbrid):
    x=numbrid[:4]
    return x
def first_and_last_4(numbrid):
    x1=numbrid[:4]
    x2=numbrid[-4:]
    return x1+x2
def odds(numbrid):
    x3=numbrid[1::2]
    return x3
def reverse_evens(numbrid):
    x3=numbrid[-1::-2]
    return x3

#or another approach
def reverse_evens(numbrid):
    x4=numbrid[::-1]
    x5=x3[::2]
    return x5

#I can't get the right outputs from the last task, even though testing in PyCharm I get the sam results as in the sample.

1 Answer

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

If you start at the end, whether you get "evens" or "odds" depends on the size of the list. So it's easy to get a false validation based on your test data.

To always get reverse events, there's two basic strategies: you can compute the reverse starting position based on the length of the list, or you can extract all the even indexed items first and then reverse them with a separate slice (and they must be done in that order).