Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.python > #106263
| From | Ian Kelly <ian.g.kelly@gmail.com> |
|---|---|
| Newsgroups | comp.lang.python |
| Subject | Re: Drowning in a teacup? |
| Date | 2016-04-01 14:52 -0600 |
| Message-ID | <mailman.333.1459543979.28225.python-list@python.org> (permalink) |
| References | <ndmlj2$pb0$1@gioia.aioe.org> <ndmmav$8n2$1@dont-email.me> |
On Fri, Apr 1, 2016 at 2:39 PM, Rob Gaddi
<rgaddi@highlandtechnology.invalid> wrote:
> Fillmore wrote:
>> Nope, wrong! contrary to what I thought I had understood about how
>> parameters are passed in Python, the function is acting on a copy(!) and
>> my original list is unchanged.
>>
>
> Nope, that's not your problem. Your problem is the line:
>
>> mylist = [mylist[i]] + mylist[:i] + mylist[i+1:]
>
> Which should be read as: "Take mylist[i], all of mylist before i,
> and all of mylist after i and create a new list from it. Store that
> new list in a variable called mylist, overwriting the previous value."
>
> If instead you were using the .insert and .remove methods, you'd be
> manipulating the existing list instead. But you don't want to do that,
> because those methods are O(N) on the list length; manipulating the
> middle of lists is slow.
Or use slice assignment. This should work in place of the above:
mylist[:] = [mylist[i]] + mylist[:i] + mylist[i+1:]
Still O(n), but so will be any implementation that removes something
from an arbitrary list position and inserts it at the front.
Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Drowning in a teacup? Fillmore <fillmore_remove@hotmail.com> - 2016-04-01 16:27 -0400
Re: Drowning in a teacup? Rob Gaddi <rgaddi@highlandtechnology.invalid> - 2016-04-01 20:39 +0000
Re: Drowning in a teacup? Ian Kelly <ian.g.kelly@gmail.com> - 2016-04-01 14:52 -0600
Re: Drowning in a teacup? MRAB <python@mrabarnett.plus.com> - 2016-04-01 21:45 +0100
Re: Drowning in a teacup? Michael Selik <michael.selik@gmail.com> - 2016-04-01 20:46 +0000
Re: Drowning in a teacup? Steven D'Aprano <steve@pearwood.info> - 2016-04-02 09:46 +1100
Re: Drowning in a teacup? Fillmore <fillmore_remove@hotmail.com> - 2016-04-02 00:03 -0400
Re: Drowning in a teacup? Vito De Tullio <vito.detullio@gmail.com> - 2016-04-02 07:45 +0200
Re: Drowning in a teacup? Michael Selik <michael.selik@gmail.com> - 2016-04-02 05:51 +0000
Re: Drowning in a teacup? Vito De Tullio <vito.detullio@gmail.com> - 2016-04-02 08:26 +0200
Re: Drowning in a teacup? Peter Otten <__peter__@web.de> - 2016-04-02 12:31 +0200
Re: Drowning in a teacup? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-04-02 12:53 +0100
Re: Drowning in a teacup? Michael Selik <michael.selik@gmail.com> - 2016-04-02 14:36 +0000
Re: Drowning in a teacup? Ned Batchelder <ned@nedbatchelder.com> - 2016-04-02 12:28 -0700
Re: Drowning in a teacup? Random832 <random832@fastmail.com> - 2016-04-02 15:54 -0400
Re: Drowning in a teacup? Steven D'Aprano <steve@pearwood.info> - 2016-04-03 12:33 +1000
Re: Drowning in a teacup? Ethan Furman <ethan@stoneleaf.us> - 2016-04-02 16:15 -0700
Re: Drowning in a teacup? Random832 <random832@fastmail.com> - 2016-04-02 19:19 -0400
csiph-web