add two lists then sort = None(?)

Question

Second list squared each item on list, xs. Running the code below, python gives me \'None\'

xs = [12, 10, 32, 3, 66, 17, 42, 99, 20]
a = [b**2 for b in xs]
c         


        

Answer 1

Generally speaking, anything that operates on something in-place will return None, by convention. (This convention is not necessarily always followed, however.) somelist.sort() will sort the list in-place.

If you'd rather have a sorted copy, you can just call c = sorted(a + xs). sorted operates on a copy of the original, and therefore returns the copy.

There's a much more through explanation here: http://wiki.python.org/moin/HowTo/Sorting/

Answer 2

You use generator expressions and itertools to reduce the amount of temporary storage like this

>>> import itertools
>>> xs = [12, 10, 32, 3, 66, 17, 42, 99, 20]
>>> a = (b**2 for b in xs)
>>> c = sorted(itertools.chain(a, xs))
>>> c
[3, 9, 10, 12, 17, 20, 32, 42, 66, 99, 100, 144, 289, 400, 1024, 1764, 4356, 9801]