determine if os.system() is done

[Xah Lee]

suppose i'm calling two system processes, one to unzip, and one to
“tail” to get the last line. How can i determine when the first
process is done?

Example:

subprocess.Pope n([r"/sw/bin/gzip","-d","access_log. 4.gz"]);

last_line=subpr ocess.Popen([r"/usr/bin/tail","-n 1","access_log. 4"],
stdout=subproce ss.PIPE).commun icate()[0]

of course, i can try workarounds something like os.system("gzip -d
thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
determine when a system process is done.

Xah
xah@xahlee.org
∑ http://xahlee.org/

[Alessandro Bottoni]

Re: determine if os.system() is done

Xah Lee wrote:[color=blue]
> of course, i can try workarounds something like os.system("gzip -d
> thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
> determine when a system process is done.[/color]

Well, if you use a function of the "popen" family, you get some kind of
return value from the subprocess on your "output" pipe. You should be able
to determine if your subprocess has terminated by examining (parsing) this
output pipe.

If you use os.system(), you should get a single return value (usually "None"
or a error code) that you can use for this task.

In both cases, you may have to use a loop (sleep(x)) to wait for the return
value (and check it) from within your code.

Have a look at the docu of the os.process module for details. (Maybe the
newer "subprocess " module is a better choice...)

HTH

-----------------------------------
Alessandro Bottoni

[Thomas Bellman]

Re: determine if os.system() is done

"Xah Lee" <xah@xahlee.org > writes:
[color=blue]
> suppose i'm calling two system processes, one to unzip, and one to
> tail to get the last line. How can i determine when the first
> process is done?[/color]
[color=blue]
> Example:[/color]
[color=blue]
> subprocess.Pope n([r"/sw/bin/gzip","-d","access_log. 4.gz"]);[/color]
[color=blue]
> last_line=subpr ocess.Popen([r"/usr/bin/tail","-n 1","access_log. 4"],
> stdout=subproce ss.PIPE).commun icate()[0][/color]
[color=blue]
> of course, i can try workarounds something like os.system("gzip -d
> thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
> determine when a system process is done.[/color]

Have you tried reading the manual for the subprocess module? You
just *might* find the answer to your question if you look at what
you can do with Popen objects. Actually, just learning about the
exact semantics of the communicate() method might be enought to
solve your problem.


--
Thomas Bellman, Lysator Computer Club, Linköping University, Sweden
"I refuse to have a battle of wits with an ! bellman @ lysator.liu.se
unarmed person." ! Make Love -- Nicht Wahr!

[Fredrik Lundh]

Re: determine if os.system() is done

Thomas Bellman wrote:
[color=blue]
> Have you tried reading the manual for the subprocess module?[/color]

han har försökt, men hans tourette tog överhanden:

http://mail.python.org/pipermail/python-list/2005-September/297642.html

</F>

[Jeremy Jones]

Re: determine if os.system() is done

Thomas Bellman wrote:
[color=blue]
>"Xah Lee" <xah@xahlee.org > writes:
>
>
>[color=green]
>>suppose i'm calling two system processes, one to unzip, and one to
>>tail to get the last line. How can i determine when the first
>>process is done?
>>
>>[/color]
>
>
>[color=green]
>>Example:
>>
>>[/color]
>
>
>[color=green]
>>subprocess.Po pen([r"/sw/bin/gzip","-d","access_log. 4.gz"]);
>>
>>[/color]
>
>
>[color=green]
>>last_line=sub process.Popen([r"/usr/bin/tail","-n 1","access_log. 4"],
>>stdout=subpro cess.PIPE).comm unicate()[0]
>>
>>[/color]
>
>
>[color=green]
>>of course, i can try workarounds something like os.system("gzip -d
>>thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
>>determine when a system process is done.
>>
>>[/color]
>
>Have you tried reading the manual for the subprocess module? You
>just *might* find the answer to your question if you look at what
>you can do with Popen objects.
>[/color]
Oh, come on. Don't you know that all Python documentation is rubbish
and not worth reading, written by IT idiots who throw around useless
jargon and indulge in extreme forms of self-gratification? Someone of
the caliber of Xah Lee would *never* stoop so low as to actually read
the documentation. It is beneath him. Instead, he posts messages to a
group of IT idiots who throw around useless jargon and indulge in
extreme forms of self-gratification in posting answers to questions.

<snip>

JMJ

[Martin Franklin]

Re: determine if os.system() is done

Xah Lee wrote:[color=blue]
> suppose i'm calling two system processes, one to unzip, and one to
> “tail” to get the last line. How can i determine when the first
> process is done?
>
> Example:
>
> subprocess.Pope n([r"/sw/bin/gzip","-d","access_log. 4.gz"]);
>
> last_line=subpr ocess.Popen([r"/usr/bin/tail","-n 1","access_log. 4"],
> stdout=subproce ss.PIPE).commun icate()[0]
>
> of course, i can try workarounds something like os.system("gzip -d
> thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
> determine when a system process is done.
>
> Xah
> xah@xahlee.org
> ∑ http://xahlee.org/
>[/color]



I think the idea is you wait for the first call to subprocess.call to
finish before executing the second...

http://docs.python.org/lib/node231.html

call( *args, **kwargs)
Run command with arguments. *Wait for command to complete*, then
return the returncode attribute.

The arguments are the same as for the Popen constructor. Example:

retcode = call(["ls", "-l"])

[Nainto]

Re: determine if os.system() is done

Yeah, I agree. The Python documentation just merey describes what
arguements a function can take not as much how to use the actual
function.

[Fredrik Lundh]

Re: determine if os.system() is done

"Nainto" <Nainto@gmail.c om> wrote:[color=blue]
> Yeah, I agree. The Python documentation just merey describes what
> arguements a function can take not as much how to use the actual
> function.[/color]

yeah, that's a really relevant criticism when we're talking about a
module that contains one function and one class, and for which the
documentation contains *sixteen* examples.

</F>

[Lars Gustäbel]

Re: determine if os.system() is done

[Fredrik Lundh][color=blue]
> han har försökt, men hans tourette tog överhanden:[/color]

IMHO it's more likely an Asperger's syndrome.

http://en.wikipedia.org/wiki/Asperger_Syndrome

--
Lars Gustäbel
lars@gustaebel. de

Any sufficiently advanced technology is indistinguishab le
from magic.
(Arthur C. Clarke)

[Steve Horsley]

Re: determine if os.system() is done

Xah Lee wrote:[color=blue]
> suppose i'm calling two system processes, one to unzip, and one to
> “tail” to get the last line. How can i determine when the first
> process is done?
>
> Example:
>
> subprocess.Pope n([r"/sw/bin/gzip","-d","access_log. 4.gz"]);
>
> last_line=subpr ocess.Popen([r"/usr/bin/tail","-n 1","access_log. 4"],
> stdout=subproce ss.PIPE).commun icate()[0]
>
> of course, i can try workarounds something like os.system("gzip -d
> thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
> determine when a system process is done.
>
> Xah
> xah@xahlee.org
> ∑ http://xahlee.org/
>[/color]

As far as I can tell from the docs (worth reading),
system(command) doesn't return until the process has completed.
It would have to do some fancy footwork to return the exit code
BEFORE the process had completed!

Steve

[Martin P. Hellwig]

Re: determine if os.system() is done

Lars Gustäbel wrote:[color=blue]
> [Fredrik Lundh]
>[color=green]
>>han har försökt, men hans tourette tog överhanden:[/color]
>
>
> IMHO it's more likely an Asperger's syndrome.
>
> http://en.wikipedia.org/wiki/Asperger_Syndrome
>[/color]

I disagree, in his writings I found no evidence of autisme.
Actually most of it can be classified as being stubborn against better
knowledge, what actually a common thing is.

But he does ask the question and by this does admits he is not
knowledged in that topic.

The only thing I am disappointed at his writing style, most likely he
has a disrupted view on social acceptable behavior and communication.
These skills might be still in development, so perhaps it is reasonable
to give him a chance and wait until he is out of his puberty.

--
mph

[Peter Hansen]

Re: determine if os.system() is done

Martin P. Hellwig wrote:[color=blue]
> The only thing I am disappointed at his writing style, most likely he
> has a disrupted view on social acceptable behavior and communication.
> These skills might be still in development, so perhaps it is reasonable
> to give him a chance and wait until he is out of his puberty.[/color]

He's 37 years old! How long should one be given to mature?

-Peter

[Xah Lee]

Re: determine if os.system() is done

Thanks all.

I found the answer, rather easily.
To make a system call and wait for it, do:

subprocess.Pope n([r"/sw/bin/gzip","-d","access_log. 4.gz"]).wait();

------
this post is archived at:

http://xahlee.org/perl-python/system_calls.html

Xah
xah@xahlee.org
∑ http://xahlee.org/


Xah Lee wrote:[color=blue]
> suppose i'm calling two system processes, one to unzip, and one to
> “tail” to get the last line. How can i determine when thefirst
> process is done?
>
> Example:
>
> subprocess.Pope n([r"/sw/bin/gzip","-d","access_log. 4.gz"]);
>
> last_line=subpr ocess.Popen([r"/usr/bin/tail","-n 1","access_log. 4"],
> stdout=subproce ss.PIPE).commun icate()[0]
>
> of course, i can try workarounds something like os.system("gzip -d
> thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
> determine when a system process is done.
>
> Xah
> xah@xahlee.org
> ∑ http://xahlee.org/[/color]

[Martin P. Hellwig]

Re: determine if os.system() is done

Peter Hansen wrote:[color=blue]
> Martin P. Hellwig wrote:
>[color=green]
>> The only thing I am disappointed at his writing style, most likely he
>> has a disrupted view on social acceptable behavior and communication.
>> These skills might be still in development, so perhaps it is
>> reasonable to give him a chance and wait until he is out of his puberty.[/color]
>
>
> He's 37 years old! How long should one be given to mature?
>[/color]
Yeah well, eeh I guess that rules out the development part.
Although puberty can take a long time (according to my SO) :-)

--
mph

[Martin Franklin]

Re: determine if os.system() is done

Xah Lee wrote:[color=blue]
> suppose i'm calling two system processes, one to unzip, and one to
> “tail” to get the las[/color]
t line. How can i determine when the first[color=blue]
> process is done?
>
> Example:
>
> subprocess.Pope n([r"/sw/bin/gzip","-d","access_log. 4.gz"]);
>
> last_line=subpr ocess.Popen([r"/usr/bin/tail","-n 1","access_log. 4"],
> stdout=subproce ss.PIPE).commun icate()[0]
>
> of course, i can try workarounds something like os.system("gzip -d
> thiss.gz && tail thiss"), but i wish to know if there's non-hack way to
> determine when a system process is done.
>
> Xah
> xah@xahlee.org
> ∑ http://xahlee.org/
>[/color]


I know you've found the answer to your question, however for the exact
example you gave a much better solution comes to mind...


import gzip

log_file = gzip.open("acce ss_log.4.gz")
last_line = log_file.readli nes()[-1]
log_file.close( )


Regards
Martin