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Python Python Collections (2016, retired 2019) Slices Back and Forth

Payam Mesgari
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Payam Mesgari
Python Web Development Techdegree Student 1,072 Points
Posted by Payam Mesgari
.a{fill-rule:evenodd;}techdegree
Payam Mesgari
Python Web Development Techdegree Student 1,072 Points

Why method chaining does not work on sort()?

Why my line fails when I try to sort the sorted_things directly after copying it, I want to do this in one line.

slices.py 
favorite_things = ['raindrops on roses', 'whiskers on kittens', 'bright copper kettles',
                   'warm woolen mittens', 'bright paper packages tied up with string',
                   'cream colored ponies', 'crisp apple strudels']

slice1 = favorite_things[1:4]
slice2 = favorite_things[len(favorite_things)-2:]
sorted_things = favorite_things[:].sort()

1 Answer

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

You have two issues here:

  • the temporary copy produced by the slice must be assigned to something or it is disposed
  • the sort method re-orders the list it is applied to, but it does not return anything

So you probably want to use the sorted function instead:

sorted_things = sorted(favorite_things[:])

And while this works, I should point out for the benefit of other readers that the challenge was expecting this to be done on 2 lines using sort.

FYI: for slice2, you don't need to compute the position using the length, a negative offset will do:

slice2 = favorite_things[-2:]