subprocess.Popen does not launch audacity

Post by Tim Johnson
Using Python 3.12.3 on Ubuntu 24.04
I've converted a legacy python2 script to python3. All went well.
However, a glitch from python2 remains.
The script uses dmenu to create menus to pick applications. Applications
are then invoked from python
using subprocess.Popen(). I have never been able to successfully launch
audacity using this approach,
which does work for other apps.
I can launch audacity successfully using dmenu_run (on its own, outside
of the script)
Popen(choice, stdout=PIPE, stderr=PIPE,
stdin=PIPE, close_fds=True)
My guess is my argument list is either insufficient or an argument is
causing the problem, but am unsure of which.
I have been retired from python programming for ten years, and am pretty
rusty, but it is still fun. There are plenty
of other ways to successfully launch audacity but it would be great to
make it work from this script.

What is the value of 'choice'?

You could try printing out the value of 'choice' for one that works and
the one that doesn't and then try them again interactively from the
Python prompt with the given values. That should eliminate all but the
essential code for easier debugging.

Tim Johnson

2025-01-10 21:00:02 UTC

,,, snipped
Popen(choice, stdout=PIPE, stderr=PIPE,
stdin=PIPE, close_fds=True)
My guess is my argument list is either insufficient or an argument is
causing the problem, but am unsure of which.
I have been retired from python programming for ten years, and am pretty
rusty, but it is still fun. There are plenty
of other ways to successfully launch audacity but it would be great to
make it work from this script.

What is the value of 'choice'?
You could try printing out the value of 'choice' for one that works
and the one that doesn't and then try them again interactively from
the Python prompt with the given values. That should eliminate all but
the essential code for easier debugging.

choice is /usr/local/bin/audacity, which is the correct path for
audacity on my system. As far as I can see, that string has no hidden bytes.

Invoking /usr/local/bin/audacity from the command line launches audacity
and so does choosing with dmenu_run. which -a audacity shows only that
item.

Maybe I need to isolate the function call and start stripping out
parameters. I should have time to do that later today.

Thanks

Left Right

2025-01-10 21:39:35 UTC

import subprocess
subprocess.run('which audacity', shell=True)

/usr/bin/audacity
CompletedProcess(args='which audacity', returncode=0)

proc = subprocess.Popen('/usr/bin/audacity',

stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE,
close_fds=True)

proc.returncode
proc.pid

53308

proc.kill()
proc.returncode

0
And I saw the interface of the program... So, in principle, what you
tried should work.

What happens if in a separate terminal you try:

$ ps auxwww | grep audacity?

Are there any processes running?

If your script fails, what is the error?

If it doesn't, can you run this:

$strace python ./audacity-test.py

where audacity-test.py looks like this:

import subprocess
proc = subprocess.Popen('/usr/local/bin/audacity',
stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE,
close_fds=True)
print(proc.returncode)
print(proc.pid)
proc.wait()
proc.kill()
print(proc.returncode)

Then, you should see something like:

clone(child_stack=NULL,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7f377d83b750) = 53932
close(10) = 0
close(8) = 0
close(6) = 0
close(3) = 0
read(9, "", 50000) = 0
close(9) = 0
write(1, "None\n", 5None
) = 5
write(1, "53932\n", 653932
) = 6
wait4(53932,

(the process id you are waiting for is going to be different of
course, but the important part is that you find the clone() call that
returns the process id your code is waiting on.)

And, if it doesn't look like the above, then show what *does* it look like.

On Fri, Jan 10, 2025 at 10:03 PM Tim Johnson via Python-list

What is the value of 'choice'?
You could try printing out the value of 'choice' for one that works
and the one that doesn't and then try them again interactively from
the Python prompt with the given values. That should eliminate all but
the essential code for easier debugging.

choice is /usr/local/bin/audacity, which is the correct path for
audacity on my system. As far as I can see, that string has no hidden bytes.
Invoking /usr/local/bin/audacity from the command line launches audacity
and so does choosing with dmenu_run. which -a audacity shows only that
item.
Maybe I need to isolate the function call and start stripping out
parameters. I should have time to do that later today.
Thanks
--
https://mail.python.org/mailman/listinfo/python-list

Gilmeh Serda

2025-01-10 21:46:53 UTC

Post by Tim Johnson
using subprocess.Popen(). I have never been able to successfully launch
audacity using this approach,

Some thoughts you might try:

What does your .desktop file say (launcher menu)? Assuming you have it
installed that way. Or is it a flatpak or something?

Read the .desktop file so you use the exact same command. It might not be
what you expected. It might need some option or it's a different command
from what you thought.

Or, try the command you used, but at the prompt, does that work? Get any
errors?

Or try something simpler, like without PIPEs, sort of back to basics, as
it were.

What's in "choice" variable? Only the (correct) command, or something else
also? Test it to be sure, it's easy to add things that shouldn't be there
in a moment of a brain fatigue.

Does it work outside your script file? For instance by invoking the Python
prompt and try there?

--
Gilmeh

They are relatively good but absolutely terrible. -- Alan Kay, commenting
on Apollos

Thomas Passin

2025-01-10 21:53:14 UTC

What is the value of 'choice'?
You could try printing out the value of 'choice' for one that works
and the one that doesn't and then try them again interactively from
the Python prompt with the given values. That should eliminate all but
the essential code for easier debugging.

choice is /usr/local/bin/audacity, which is the correct path for
audacity on my system. As far as I can see, that string has no hidden
bytes.
Invoking /usr/local/bin/audacity from the command line launches audacity
and so does choosing with dmenu_run. which -a audacity shows only that
item.
Maybe I need to isolate the function call and start stripping out
parameters. I should have time to do that later today.

I don't know why you would want to redirect stdin, etc. It's a GUI
application.

from subprocess import run
run('/usr/bin/audacity')

Tim Johnson

2025-01-10 23:21:21 UTC

,,, snipped
Popen(choice, stdout=PIPE, stderr=PIPE,
stdin=PIPE, close_fds=True)
My guess is my argument list is either insufficient or an argument is
causing the problem, but am unsure of which.
I have been retired from python programming for ten years, and am
pretty
rusty, but it is still fun. There are plenty
of other ways to successfully launch audacity but it would be great to
make it work from this script.

What is the value of 'choice'?
You could try printing out the value of 'choice' for one that works
and the one that doesn't and then try them again interactively from
the Python prompt with the given values. That should eliminate all
but the essential code for easier debugging.

choice is /usr/local/bin/audacity, which is the correct path for
audacity on my system. As far as I can see, that string has no hidden
bytes.
Invoking /usr/local/bin/audacity from the command line launches
audacity and so does choosing with dmenu_run. which -a audacity
shows only that item.
Maybe I need to isolate the function call and start stripping out
parameters. I should have time to do that later today.

I don't know why you would want to redirect stdin, etc. It's a GUI
application.