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Groups > comp.lang.python > #90807 > unrolled thread
| Started by | Mario Figueiredo <marfig@gmail.com> |
|---|---|
| First post | 2015-05-18 20:23 +0100 |
| Last post | 2015-05-19 22:51 +0300 |
| Articles | 3 on this page of 83 — 21 participants |
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Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-18 20:23 +0100
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-19 05:36 +1000
Re: Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-18 20:49 +0100
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-19 06:04 +1000
Re: Slices time complexity Todd <toddrjen@gmail.com> - 2015-05-18 21:42 +0200
Re: Slices time complexity Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-18 13:49 -0600
Re: Slices time complexity Fabien <fabien.maussion@gmail.com> - 2015-05-18 21:54 +0200
Re: Slices time complexity Todd <toddrjen@gmail.com> - 2015-05-18 22:23 +0200
Re: Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-18 22:04 +0100
Re: Slices time complexity Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-18 22:38 +0100
Re: Slices time complexity Terry Reedy <tjreedy@udel.edu> - 2015-05-18 19:04 -0400
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-18 19:20 -0700
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 15:13 +1000
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-18 22:33 -0700
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 10:12 +0300
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 18:16 +1000
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 11:39 +0300
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-19 18:50 +1000
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 12:35 +0300
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 23:44 +1000
Re: Slices time complexity Christian Gollwitzer <auriocus@gmx.de> - 2015-05-20 23:54 +0200
Re: Slices time complexity Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-19 23:00 +1200
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 11:47 +1000
Re: Slices time complexity Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-05-20 08:07 -0400
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 22:42 +1000
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-19 23:24 +1000
Re: Slices time complexity Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-20 12:31 +1200
Re: Slices time complexity Ben Finney <ben+python@benfinney.id.au> - 2015-05-20 10:42 +1000
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 07:24 +0300
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 21:30 -0700
Re: Slices time complexity Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-20 06:06 +0100
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 15:57 +1000
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 09:17 +0300
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 23:23 -0700
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 09:46 +0300
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-20 00:03 -0700
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 10:45 +0300
List semantics [was Re: Slices time complexity] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 17:23 +1000
Re: List semantics [was Re: Slices time complexity] Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-20 20:54 +1200
Re: List semantics [was Re: Slices time complexity] Ned Batchelder <ned@nedbatchelder.com> - 2015-05-20 04:08 -0700
Re: List semantics [was Re: Slices time complexity] Terry Reedy <tjreedy@udel.edu> - 2015-05-20 14:42 -0400
Re: List semantics [was Re: Slices time complexity] Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-21 11:06 +1200
Re: List semantics [was Re: Slices time complexity] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-21 12:10 +1000
Re: Slices time complexity "Bartc" <bartc@freeuk.com> - 2015-05-20 10:56 +0100
Re: Slices time complexity Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-20 10:16 +0100
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-21 15:19 +1000
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-21 09:20 +0300
Re: Slices time complexity bartc <bart4858@gmail.com> - 2015-05-21 06:34 -0700
Re: Slices time complexity MRAB <python@mrabarnett.plus.com> - 2015-05-21 17:50 +0100
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-22 03:16 +1000
Re: Slices time complexity bart4858@gmail.com - 2015-05-21 12:48 -0700
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 12:26 +1000
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-20 12:36 +1000
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 20:02 -0700
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 21:43 +1000
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 18:59 +0300
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 03:46 +1000
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-20 04:12 +1000
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 21:19 +0300
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 10:43 +1000
Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 07:30 +0300
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 15:33 +1000
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 15:58 +1000
Re: Slices time complexity Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-19 15:18 +0100
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 04:46 -0700
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 05:14 -0700
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 18:19 +1000
Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 04:41 -0700
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 19:45 +1000
Re: Slices time complexity Serhiy Storchaka <storchaka@gmail.com> - 2015-05-19 13:15 +0300
Re: Slices time complexity Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-19 12:09 +0100
Re: Slices time complexity "Bartc" <bartc@freeuk.com> - 2015-05-19 15:52 +0100
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 03:07 +1000
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-20 03:19 +1000
Re: Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-20 20:51 +0100
Re: Slices time complexity Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-20 14:33 -0600
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-21 06:35 +1000
Re: Slices time complexity Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-20 21:47 +0100
Re: Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-20 22:23 +0100
Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-21 17:35 +1000
Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-21 18:25 +1000
Re: Slices time complexity Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-19 09:15 -0600
Re: Slices time complexity Serhiy Storchaka <storchaka@gmail.com> - 2015-05-19 22:51 +0300
Page 5 of 5 — ← Prev page 1 2 3 4 [5]
| From | Chris Angelico <rosuav@gmail.com> |
|---|---|
| Date | 2015-05-21 18:25 +1000 |
| Message-ID | <mailman.194.1432196751.17265.python-list@python.org> |
| In reply to | #91000 |
On Thu, May 21, 2015 at 5:35 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
>> You don't need huge. On any algorithm where slices are being used you
>> will have to account for the linear complexity. You seem to be
>> dismissive of this fact, but it can have tremendous performance
>> implications, since it can turn a linear algorithm into a quadratic
>> one just like that.
>
> Sure. And for small enough N, everything is fast.
>
> There's a sorting algorithm, usually called "Bozo sort", which shuffles the
> list, then checks whether it is sorted. If not, it shuffles it again, until
> it is sorted. Bozo sort is a *terrible* algorithm, with no upper limit to
> the worst case, and O(N!) for the average case. And yet, with small lists
> (say, five items) the performance is acceptable if your requirements are
> low.
A less ridiculous, but equally valid, comparison is with
multiplication algorithms. A while ago someone asked about what Python
uses, and on learning that CPython uses Karatsuba [1], suggested that
some other algorithm (I don't remember which) had better asymptotic
complexity. Downside: It'd be slower for smaller numbers, and the
complexity cost of an additional cutoff ("use grade-school up to X,
then Karatsuba up to Y, then Fuerer's") would also negatively impact
performance overall. Grade-school arithmetic is O(N*N) which looks
terrible... but for smallish numbers, its performance is quite
adequate.
ChrisA
[1] https://en.wikipedia.org/wiki/Karatsuba_algorithm
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| From | Ian Kelly <ian.g.kelly@gmail.com> |
|---|---|
| Date | 2015-05-19 09:15 -0600 |
| Message-ID | <mailman.141.1432048556.17265.python-list@python.org> |
| In reply to | #90837 |
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On May 19, 2015 4:16 AM, "Serhiy Storchaka" <storchaka@gmail.com> wrote: > > On 19.05.15 12:45, Steven D'Aprano wrote: >> >> On Tuesday 19 May 2015 05:23, Mario Figueiredo wrote: >>> >>> From the above link it seems slices work in linear time on all cases. >> >> >> I wouldn't trust that is always the case, e.g. deleting a contiguous slice >> from the end of a list could be O(1). > > > It always has linear complexity. You need to decref removed elements. Only in CPython. The operation might be O(1) in Pypy or Jython.
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| From | Serhiy Storchaka <storchaka@gmail.com> |
|---|---|
| Date | 2015-05-19 22:51 +0300 |
| Message-ID | <mailman.153.1432065079.17265.python-list@python.org> |
| In reply to | #90837 |
On 19.05.15 18:15, Ian Kelly wrote: > On May 19, 2015 4:16 AM, "Serhiy Storchaka" <storchaka@gmail.com > <mailto:storchaka@gmail.com>> wrote: > > > > On 19.05.15 12:45, Steven D'Aprano wrote: > >> > >> On Tuesday 19 May 2015 05:23, Mario Figueiredo wrote: > >>> > >>> From the above link it seems slices work in linear time on all cases. > >> > >> > >> I wouldn't trust that is always the case, e.g. deleting a contiguous > slice > >> from the end of a list could be O(1). > > > > > > It always has linear complexity. You need to decref removed elements. > > Only in CPython. The operation might be O(1) in Pypy or Jython. In any case you need linear time to free all objects.
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