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

Posted by mellowmushroom
mellowmushroom
9,250 Points

for create function reverse_evens, how come this is not acceptable: def reverse_evens(iter): return iter[::-2]

for create function reverse_evens, how come this is not acceptable: def reverse_evens(iter): return iter[::-2]

slices.py 
def first_4(iterable):
    return iterable[:4]
def first_and_last_4(iterable):
    first_4 = iterable[:4]
    last_number = iterable[-1:]
    last_3 = iterable[-4:-1]
    last_4 = last_3 + last_number

    added = first_4 + last_4
    return added
def odds(iterable):
    return iterable[1::2]
def reverse_evens(iterable):
    return iterable[::-2]

3 Answers

Steven Parker
Steven Parker
231,007 Points
Steven Parker
Steven Parker
231,007 Points

You don't know if you're getting evens or odds.

That would certainly give you every other item in reverse, but whether those items are from the even indexes or the odd indexes would depend on how long the list is.

You'll need to either compute where to start based on the length, or you'll need to get the evens first and then reverse them in a separate operation (perhaps by using two slices).

Dean Meyer
Dean Meyer
1,378 Points

Hi Steven

I kinda see where you are getting at, however, I just keep getting it wrong. Do you mind sharing your code with over here (the even odd slicing question). Would be great!

Thanks!

mellowmushroom
mellowmushroom
9,250 Points
mellowmushroom
mellowmushroom
9,250 Points

oh ok thanks!

mellowmushroom
mellowmushroom
9,250 Points
mellowmushroom
mellowmushroom
9,250 Points

Hey Dean,

this is how I ended up implementing the function:

def reverse_evens(itera):
    count = 0
    for i in itera:
        count = count + 1
    if count % 2 == 0:
        print(itera[-2::-2])
        return itera[-2::-2]
    else:
        print(itera[::-2])
        return itera[::-2]
Steven Parker
Steven Parker
231,007 Points
Steven Parker
Steven Parker
231,007 Points

You don't need to print anything for this challenge. But otherwise, good job. :+1: