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

Posted by Scott Ewing
Scott Ewing
3,107 Points

Why doesn't "sorted_things = favorite_things[:].sort()" create a sorted copy in sorted_things?

I tried to use a one-line assignment to create the sorted list of 'sorted_things' but it doesn't work. It seems that favorite_things[:].sort() returns a NoneType when I would expect it to return a list.

ex: 

>>> 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']

The result is what is expected here:

>>> 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']

Now if we try and sort this in-line we get nothing:

>>> favorite_things[:].sort()
>>>

If we assign this to a variable, we still get nothing:

>>> sorted_things = favorite[:].sort()
>>>
>>> print(sorted_things)
None
>>>

1 Answer

Steven Parker
Steven Parker
231,236 Points
Steven Parker
Steven Parker
231,236 Points

Well, "sort()" might not work as you expect. It directly sorts the thing you apply it to, but doesn't actually return anything. And since you were applying it to an anonymous slice, there was no evidence left of what it did.

You probably want to use "sorted()" instead, it returns a sorted version of its (unchanged) argument:

sorted_things = sorted(favorite_things)