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

yannis sousanis
yannis sousanis
7,199 Points
Posted by yannis sousanis
yannis sousanis
7,199 Points

help with strings

on the functions reverse_evens I used return a[-1:0:2] where -1 starts at the end where 0 stops at the begining and 2 for steps But it doesnt work

slices.py 
def first_4(a):  
    return a[0:4]
def first_and_last_4(a):
    return a[0:4] + a[-4:len(a)]
def odds(a):
    return a[1::2]
def reverse_evens(a):
    return a[-1:0:2]

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

Keep in mind that the list of items might have an even or odd number of items. Therefore it is necessary to break the slice into two parts: Getting the even-indexed and then reversing the list. Slices can also be changed like by stacking the square brackets: somelist[slice1][slice2]

Post back if you need more help. Good luck!!

Namrata Lamba
Namrata Lamba
1,347 Points

Hi Chris,

Why is this not working?

return item[0::2:-1]

Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

Namrata, the slice item[0::2:-1] is not legal syntax. An individual slice can only have [start:stop:step] format. To stack slices, use item[start:stop:step][start:stop:step] format