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
xa*@xahlee.org
∑ http://xahlee.org/

[Alessandro Bottoni]

Xah Lee wrote:

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.

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]

"Xah Lee" <xa*@xahlee.org > writes:

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.

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]

Thomas Bellman wrote:

Have you tried reading the manual for the subprocess module?

han har försökt, men hans tourette tog överhanden:

http://mail.python.org/pipermail/pyt...er/297642.html

</F>

[Jeremy Jones]

Thomas Bellman wrote:

"Xah Lee" <xa*@xahlee.org > writes:

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.Po pen([r"/sw/bin/gzip","-d","access_log. 4.gz"]);

last_line=sub process.Popen([r"/usr/bin/tail","-n 1","access_log. 4"],
stdout=subpro cess.PIPE).comm unicate()[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.

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.

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]

Xah Lee wrote:

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
xa*@xahlee.org
∑ http://xahlee.org/

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]

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]

"Nainto" <Na****@gmail.c om> wrote:

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

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]

[Fredrik Lundh]

han har försökt, men hans tourette tog överhanden:

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

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

--
Lars Gustäbel
la**@gustaebel. de

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

[Steve Horsley]

Xah Lee wrote:

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
xa*@xahlee.org
∑ http://xahlee.org/

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