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| Date | Fri, 5 Jun 2015 07:44:25 +1000 |
| Subject | Re: Can Python function return multiple data? |
| From | Chris Angelico <rosuav@gmail.com> |
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On Fri, Jun 5, 2015 at 3:11 AM, Steven D'Aprano <steve@pearwood.info> wrote:
> You need at least one more test to prove pass by value: you need to
> demonstrate that the value bound to y is copied when passed to the
> function. E.g. pass a mutable value (say, a list) and mutate it inside the
> function. If the list in the outer scope is *not* mutated, then and only
> then can you say it is pass by value.
Minor quibble: This discussion is about semantics, not timing. A
language can use pass-by-value but with optimizations for the
read-only case.
$ cat array_argument.php
<?php
function readonly($arr) {if ($arr[1] != 1) echo "WRONG!\n";}
function readwrite($arr) {$arr[1] = 1;}
$array = array();
//Populate a big array
for ($i=0; $i<1000; ++$i) $array[$i] = $i;
//Now pass it repeatedly as an argument
$start = microtime(1);
for ($i=0; $i<100000000; ++$i) readonly($array);
$i/=1000000;
$t = (microtime(1)-$start);
echo "Read-only: $i million iterations in $t seconds\n";
$start = microtime(1);
for ($i=0; $i<100000; ++$i) readwrite($array);
$i/=1000;
$t = (microtime(1)-$start);
echo "Read-write: $i thousand iterations in $t seconds\n";
$ time php array_argument.php
Read-only: 100 million iterations in 11.251608133316 seconds
Read-write: 100 thousand iterations in 2.6384630203247 seconds
real 0m13.914s
user 0m13.780s
sys 0m0.000s
PHP passes arrays by value, but optimizes away the copy in the
read-only case - which means that array mutations can trigger
unexpected copying. But it's still pass-by-value, even though you can
appear to have the performance of pass-by-object/pass-by-reference.
Conceivably, a language might implement pass-by-value by having a
"shadow" that knows that it's "the same as that array only this one
got changed", although I can't imagine it'd be efficient for
real-world work. It'd still be legitimate pass-by-value though.
ChrisA
Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Can Python function return multiple data? fl <rxjwg98@gmail.com> - 2015-06-02 14:27 -0700
Re: Can Python function return multiple data? Joel Goldstick <joel.goldstick@gmail.com> - 2015-06-02 17:35 -0400
Re: Can Python function return multiple data? sohcahtoa82@gmail.com - 2015-06-02 14:40 -0700
Re: Can Python function return multiple data? John Gordon <gordon@panix.com> - 2015-06-02 21:40 +0000
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-03 09:56 +1000
Re: Can Python function return multiple data? Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2015-06-03 15:56 +0200
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-04 07:35 +1000
Re: Can Python function return multiple data? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-03 22:56 +0100
Re: Can Python function return multiple data? sohcahtoa82@gmail.com - 2015-06-03 15:28 -0700
Re: Can Python function return multiple data? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-06-03 21:30 -0400
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-04 11:52 +1000
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-04 23:47 +1000
Re: Can Python function return multiple data? Marko Rauhamaa <marko@pacujo.net> - 2015-06-04 17:25 +0300
Re: Can Python function return multiple data? Grant Edwards <invalid@invalid.invalid> - 2015-06-04 14:37 +0000
Re: Can Python function return multiple data? Marko Rauhamaa <marko@pacujo.net> - 2015-06-04 18:04 +0300
Re: Can Python function return multiple data? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-06-04 19:51 -0400
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 03:11 +1000
Re: Can Python function return multiple data? Marko Rauhamaa <marko@pacujo.net> - 2015-06-04 20:30 +0300
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 08:37 +1000
Re: Can Python function return multiple data? random832@fastmail.us - 2015-06-04 13:30 -0400
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 08:31 +1000
Re: Can Python function return multiple data? Grant Edwards <invalid@invalid.invalid> - 2015-06-04 18:38 +0000
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 08:52 +1000
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-05 09:04 +1000
Re: Can Python function return multiple data? Grant Edwards <invalid@invalid.invalid> - 2015-06-05 02:02 +0000
Re: Can Python function return multiple data? Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-06-05 09:11 +0200
Re: Can Python function return multiple data? Marko Rauhamaa <marko@pacujo.net> - 2015-06-05 12:27 +0300
Re: Can Python function return multiple data? Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-06-05 14:04 +0200
Re: Can Python function return multiple data? BartC <bc@freeuk.com> - 2015-06-04 21:52 +0100
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 09:13 +1000
Re: Can Python function return multiple data? BartC <bc@freeuk.com> - 2015-06-05 01:16 +0100
Re: Can Python function return multiple data? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-05 02:40 +0100
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 11:48 +1000
Re: Can Python function return multiple data? BartC <bc@freeuk.com> - 2015-06-05 11:06 +0100
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-05 07:44 +1000
Re: Can Python function return multiple data? BartC <bc@freeuk.com> - 2015-06-05 10:51 +0100
Re: Can Python function return multiple data? ElChino <elchino@cnn.cn> - 2015-06-04 17:37 +0200
Re: Can Python function return multiple data? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-06-04 19:57 -0400
Re: Can Python function return multiple data? random832@fastmail.us - 2015-06-04 13:26 -0400
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 08:16 +1000
Re: Can Python function return multiple data? random832@fastmail.us - 2015-06-04 18:59 -0400
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 12:37 +1000
Re: Can Python function return multiple data? Rustom Mody <rustompmody@gmail.com> - 2015-06-04 20:16 -0700
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 21:06 +1000
Re: Can Python function return multiple data? Rustom Mody <rustompmody@gmail.com> - 2015-06-05 06:29 -0700
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-06 07:59 +1000
Re: Can Python function return multiple data? Rustom Mody <rustompmody@gmail.com> - 2015-06-05 20:20 -0700
Re: Can Python function return multiple data? random832@fastmail.us - 2015-06-05 23:28 -0400
Re: Can Python function return multiple data? Rustom Mody <rustompmody@gmail.com> - 2015-06-05 22:28 -0700
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-06 15:43 +1000
Lawful != Mutable (was Can Python function return multiple data?) Rustom Mody <rustompmody@gmail.com> - 2015-06-07 08:49 -0700
Re: Lawful != Mutable (was Can Python function return multiple data?) Chris Angelico <rosuav@gmail.com> - 2015-06-08 02:07 +1000
Re: Lawful != Mutable (was Can Python function return multiple data?) Rustom Mody <rustompmody@gmail.com> - 2015-06-07 09:20 -0700
Re: Lawful != Mutable (was Can Python function return multiple data?) Chris Angelico <rosuav@gmail.com> - 2015-06-08 02:34 +1000
Re: Lawful != Mutable (was Can Python function return multiple data?) Rustom Mody <rustompmody@gmail.com> - 2015-06-20 18:59 -0700
Re: Lawful != Mutable (was Can Python function return multiple data?) Chris Angelico <rosuav@gmail.com> - 2015-06-21 12:32 +1000
Re: Lawful != Mutable (was Can Python function return multiple data?) Rustom Mody <rustompmody@gmail.com> - 2015-06-20 19:50 -0700
Re: Lawful != Mutable (was Can Python function return multiple data?) Laura Creighton <lac@openend.se> - 2015-06-21 11:14 +0200
Re: Lawful != Mutable (was Can Python function return multiple data?) Ron Adam <ron3200@gmail.com> - 2015-06-21 08:55 -0400
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-07 15:51 +1000
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-06 13:49 +1000
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-06 14:50 +1000
Re: Can Python function return multiple data? Chris Angelico <rosuav@gmail.com> - 2015-06-06 15:29 +1000
Re: Can Python function return multiple data? Rustom Mody <rustompmody@gmail.com> - 2015-06-05 22:32 -0700
Re: Can Python function return multiple data? Dave Farrance <df@see.replyto.invalid> - 2015-06-06 07:52 +0100
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-07 15:53 +1000
Re: Can Python function return multiple data? random832@fastmail.us - 2015-06-05 08:21 -0400
Re: Can Python function return multiple data? Marko Rauhamaa <marko@pacujo.net> - 2015-06-05 16:37 +0300
Re: Can Python function return multiple data? Rustom Mody <rustompmody@gmail.com> - 2015-06-04 19:07 -0700
Re: Can Python function return multiple data? Michael Torrie <torriem@gmail.com> - 2015-06-04 11:36 -0600
Re: Can Python function return multiple data? random832@fastmail.us - 2015-06-04 13:51 -0400
Re: Can Python function return multiple data? Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-06-04 20:17 +0200
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-05 08:45 +1000
Re: Can Python function return multiple data? Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-06-05 08:59 +0200
Re: Can Python function return multiple data? Michael Torrie <torriem@gmail.com> - 2015-06-04 08:16 -0600
Re: Can Python function return multiple data? sohcahtoa82@gmail.com - 2015-06-05 11:55 -0700
Re: Can Python function return multiple data? random832@fastmail.us - 2015-06-04 01:01 -0400
Re: Can Python function return multiple data? Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-04 12:34 -0600
Re: Can Python function return multiple data? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-04 20:16 +0100
Re: Can Python function return multiple data? Serhiy Storchaka <storchaka@gmail.com> - 2015-06-04 09:56 +0300
Re: Can Python function return multiple data? fl <rxjwg98@gmail.com> - 2015-06-06 10:57 -0700
Re: Can Python function return multiple data? Rustom Mody <rustompmody@gmail.com> - 2015-06-06 21:35 -0700
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-07 15:47 +1000
Re: Can Python function return multiple data? Steven D'Aprano <steve@pearwood.info> - 2015-06-07 15:33 +1000
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