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Groups > comp.lang.python > #48747
| Date | 2013-06-19 12:57 -0700 |
|---|---|
| From | Gary Herron <gherron@digipen.edu> |
| Subject | Re: Default Value |
| References | <7e6361d5-6619-4aaa-adda-8b5f01bde57f@googlegroups.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.3597.1371672307.3114.python-list@python.org> (permalink) |
On 06/19/2013 12:17 PM, Ahmed Abdulshafy wrote:
> I'm reading the Python.org tutorial right now, and I found this part rather strange and incomprehensible to me>
>
> Important warning: The default value is evaluated only once. This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes
This code:
> def f(a, L=[]):
> L.append(a)
> return L
does the same as this code:
M=[]
def f(a, L=M):
L.append(a)
return L
where it's slightly more obvious that the list is created once, and
modified with each call to the function (or rather with each call to the
function that does not supply its own value for L).
Gary Herron
>
> print(f(1))
> print(f(2))
> print(f(3))
>
> This will print
> [1]
> [1, 2]
> [1, 2, 3]
>
> How the list is retained between successive calls? And why?
--
Dr. Gary Herron
Department of Computer Science
DigiPen Institute of Technology
(425) 895-4418
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Default Value Ahmed Abdulshafy <abdulshafy@gmail.com> - 2013-06-19 12:17 -0700
Re: Default Value Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-06-19 22:35 +0300
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-19 12:38 -0700
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 05:57 -0700
Re: Default Value Roy Smith <roy@panix.com> - 2013-06-20 09:19 -0400
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 06:31 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 00:17 +0000
Re: Default Value Roy Smith <roy@panix.com> - 2013-06-20 20:25 -0400
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-20 07:49 -0700
Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-21 01:38 +1000
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-20 11:05 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 00:57 +0000
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-20 20:16 -0700
Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-21 17:10 +1000
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 07:32 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 16:22 +0000
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 15:57 +0000
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 10:01 -0700
Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-21 18:47 +0100
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 11:26 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 18:37 +0000
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 12:18 -0700
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 12:35 -0700
Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 05:07 +1000
Re: Default Value Neil Cerutti <neilc@norwich.edu> - 2013-06-21 19:20 +0000
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 13:27 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-22 01:31 +0000
Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 11:40 +1000
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 18:42 -0700
Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-22 03:04 +0100
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 19:32 -0700
Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-22 20:36 +0100
Re: Default Value Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-06-22 18:51 -0400
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-21 19:43 -0700
Re: Default Value Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-06-22 09:26 +0100
Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-21 20:25 +0100
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 13:44 -0700
Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-21 23:49 +0100
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 16:51 -0700
Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-22 02:54 +0100
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-22 01:15 +0000
Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-21 19:27 -0600
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-21 19:32 -0700
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 19:55 -0700
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-21 23:23 -0700
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-22 08:07 -0700
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-22 08:31 -0700
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-22 09:11 -0700
Re: Default Value Grant Edwards <invalid@invalid.invalid> - 2013-06-24 14:22 +0000
Re: [SPAM] Re: Default Value MRAB <python@mrabarnett.plus.com> - 2013-06-24 16:22 +0100
Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 11:41 +1000
Re: Default Value Michael Torrie <torriem@gmail.com> - 2013-06-21 20:46 -0600
Re: Default Value Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-06-22 16:40 +0200
Re: Default Value Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-06-22 12:49 -0400
Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-22 12:57 -0600
Re: Default Value Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-06-22 18:48 -0400
Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-22 00:40 +0100
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 18:15 -0700
Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 11:37 +1000
Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-21 19:42 -0600
Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-21 19:38 -0600
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 19:40 -0700
Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-22 03:01 +0100
Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-22 12:18 +1000
Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-22 03:25 +0100
Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-22 18:19 +0100
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-22 11:49 -0700
Re: Default Value Rotwang <sg552@hotmail.co.uk> - 2013-06-23 01:49 +0100
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 10:12 -0700
Re: Default Value Chris Angelico <rosuav@gmail.com> - 2013-06-21 03:19 +1000
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 10:30 -0700
Re: Default Value Ian Kelly <ian.g.kelly@gmail.com> - 2013-06-20 11:57 -0600
Re: Default Value rusi <rustompmody@gmail.com> - 2013-06-20 11:15 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 01:08 +0000
Re: Default Value Tim Chase <python.list@tim.thechases.com> - 2013-06-20 20:26 -0500
Re: Default Value Roy Smith <roy@panix.com> - 2013-06-20 21:40 -0400
Re: Default Value Tim Chase <python.list@tim.thechases.com> - 2013-06-20 21:02 -0500
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-20 11:07 -0700
Re: Default Value alex23 <wuwei23@gmail.com> - 2013-06-21 10:55 +1000
Re: Default Value 88888 Dihedral <dihedral88888@gmail.com> - 2013-06-20 19:18 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 02:26 +0000
Re: Default Value "Lefavor, Matthew (GSFC-582.0)[MICROTEL LLC]" <matthew.lefavor@nasa.gov> - 2013-06-20 17:28 -0500
Re: Default Value Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-21 08:17 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-21 01:28 +0000
Re: Default Value Gary Herron <gherron@digipen.edu> - 2013-06-19 12:57 -0700
Re: Default Value Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-20 01:17 +0000
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