Use multiple functions at once on a list

Question

Basically, I have a list and I want to perform multiple functions on it at once. For example,

List = [1,2,3,4,5]
List.extend([1,2,3,4,5]).sort().reverse()

I would like the result to be [5,5,4,4,3,3,2,2,1,1].

I haven't used Python in a while, but I know I've done something like this before. Is it something simple I'm missing or what?

It has to all be on one line by the way.

Trust me, if the requirements weren't that it had to be all on one line this would be much easier. But I guess it's about learning to condense code. — Stephen Roda, Aug 29 '12 at 04:39
If you are learning Python, you should learn that sometimes you need uncondense code to emphasize readability over terseness. — BrenBarn, Aug 29 '12 at 04:41
if you want to really piss some people off, use semicolons, and chain the commands lol — notbad.jpeg, Aug 29 '12 at 04:42
I agree that learning to condense the code before actually knowing how it works is kind of pointless. But it's a tradeoff; getting higher grades or actually learning the material. I know that learning the material is more important in the long run, but grades are also important. Today's educational system I guess :/ — Stephen Roda, Aug 29 '12 at 04:45
@BrenBarn, I'm not asking you to do it, I just thought there was a way to use multiple functions on one line. Thanks for the input though.. — Stephen Roda, Aug 29 '12 at 05:09

score 7 · Accepted Answer · edited May 23 '17 at 11:56

7

Most Python methods that mutate a container in-place return None

However your example can easily be handled in one line

L = [1,2,3,4,5]
L = sorted(L+[1,2,3,4,5], reverse=True)

Keeping in the spirit of the challenge, it's not hard to chain the operations (because they always return None)

>>> L = [1, 2, 3, 4, 5]
>>> L.extend([1,2,3,4,5]) or L.sort() or L.reverse() or L
[5, 5, 4, 4, 3, 3, 2, 2, 1, 1]

Here's another way

>>> L = [1, 2, 3, 4, 5]
>>> (L.extend([1,2,3,4,5]), L.sort(), L.reverse()) and L
[5, 5, 4, 4, 3, 3, 2, 2, 1, 1]

And you can let your imagination run wild

>>> L = [1, 2, 3, 4, 5]
>>> max(L.extend([1,2,3,4,5]), L.sort(), L.reverse(), L) # Python2.x only
[5, 5, 4, 4, 3, 3, 2, 2, 1, 1]

edited May 23 '17 at 11:56

Community

1
1

answered Aug 29 '12 at 04:43

John La Rooy

295,403
53
369
502

3

These are pretty *ugly* tricks producing unreadable code for non-Python gurus and therefore deserves a downvote...no trickery please – Aug 29 '12 at 05:18
I actually like this answer, but I'm quite new to Python. Are the commas ugly tricks too? I think they're pretty useful. – Stephen Roda Aug 29 '12 at 05:28
I agree with @esaelPsnoroMoN: Do as you want at home, but don't advertise it. -1. – Pierre GM Aug 29 '12 at 08:59

score 4 · Answer 2 · edited Aug 29 '12 at 04:42

4

You cannot chain the above operations since they are performed in-place. As alternatives, use sorted() and reversed().

edited Aug 29 '12 at 04:42

Ry-

218,210
55
464
476

answered Aug 29 '12 at 04:39

And why exactly in-place operations prevent chaining? If `sort` and `reverse` had returned reference to the original list, the example in the OP would be possible. – rkhayrov Aug 29 '12 at 04:41
Why do you want to argue? As said: the methods are *in-place* and there result is None. So it is obviously that you can not chain *POINT* – Aug 29 '12 at 04:42
1

@esaelPsnoroMoN Because it's precision that matters. The lack of return value prevents chaining, not in-place operation. – rkhayrov Aug 29 '12 at 04:43
1

@rkhayrov, The are detailed reasons for the decision on the Python dev list some time last century – John La Rooy Aug 29 '12 at 04:45
2

@esaelPsnoroMoN I find your comments not constructive, and borderline offensive. If you haven't noticed, I am not an OP. I haven't suggested that Python does this wrong. I've only pointed out that your answer contains logical fallacy. – rkhayrov Aug 29 '12 at 05:18

Burhan Khalid · Answer 3 · 2012-08-29T05:01:28.193

4

How about:

>>> l = [1,2,3,4,5]*2
>>> l.sort(reverse=True)
>>> l
[5, 5, 4, 4, 3, 3, 2, 2, 1, 1]

Or even shorter:

>>> sorted([1,2,3,4,5]*2,reverse=True)
[5, 5, 4, 4, 3, 3, 2, 2, 1, 1]

edited Aug 29 '12 at 05:01

answered Aug 29 '12 at 04:43

Burhan Khalid

169,990
18
245
284

score 1 · Answer 4 · answered Aug 29 '12 at 04:40

1

Each of those functions acts on the list in-place, returning None and not the modified list. You'd have to do something like

l = [1,2,3,4,5]
l = reversed(sorted(l + [1,2,3,4,5]))

answered Aug 29 '12 at 04:40

chepner

497,756
71
530
681

score 1 · Answer 5 · answered Aug 29 '12 at 07:13

Not perfect but interesting..

class chain():
    def __init__(self, my_object):
        self.o = my_object

    def __getattr__(self, attr):
        x = getattr(self.o, attr)
        if hasattr(x, '__call__'):
            method = x
            return lambda *args: self if method(*args) is None else method(*args)
        else:
            prop = x
            return prop

list_ = chain([1, 2, 3, 0])
print list_.extend([9,5]).sort().reverse()

score 0 · Answer 6 · answered Aug 29 '12 at 04:43

The functions extend, sort and reverse doesn't return list but change the list on which they are called. Chaining relies on a fact that previous function returns some value and works on it.

E.g. s="abc" then you can do s.upper().lower() as .upper() return a new string in uppercase (ans same for .lower()).

Use multiple functions at once on a list

6 Answers6