Cannot launching app with python's subprocess.call method gives error

jiceq · 07-24-2015, 06:27 AM

Hi,
i'm new to the forum and i hope u guys can help me out.

I'm working with centos 7 gnome desktop and i'm writing a python script that runs inside Autodesk Maya. All works well until the time when i want to launch programmatically a video player.

i'm doing this:

Code:

command6 = "gnome-terminal -x bash -c 'melt /home/jiceq/Desktop/pelota.mov;bash'"
subprocess.call(command6, shell=True, env=os.environ.copy(),stdout=PIPE)

The application is the melt video engine and if i type this on the command line:

Code:

melt /home/jiceq/Desktop/pelota.mov

the video starts correctly so it works perfectly from there. Conversely, if i do it from python it gives me an error.

Code:

mlt_repository_init: failed to dlopen /usr/lib64/mlt/libmltavformat.so
  (/lib64/libavfilter.so.4: symbol sws_isSupportedEndiannessConversion, version LIBSWSCALE_2 not defined in file libswscale.so.2 with link time reference)
No LADSPA plugins were found!

Check your LADSPA_PATH environment variable.

I'm quite convinced the configuration from the gnome-terminal is not the correct one. Maybe the command6 is incorrect.

I've tried to launch other installed programs and they fail to launch from python but not from the command line.

Can u give me a hint on this?

Maybe this isnt the right spot maybe it should be on programming forum...

grail · 07-24-2015, 10:34 AM

What happens when you type the command as you have it in the python script onto the command line?

Code:

bash -c 'melt /home/jiceq/Desktop/pelota.mov;bash'

# and then
gnome-terminal -x bash -c 'melt /home/jiceq/Desktop/pelota.mov;bash'

Also, it is a good practice in scripts to use the full path to a command to make sure the correct one is called.

the other thing to check would be where is LADSPA_PATH being set and is it available as you invoke bash several times in the call.

dugan · 07-24-2015, 11:38 AM

subprocess.call takes the command and its arguments as a list, not as a single string. So at the very least it should be:

Code:

command6 = ['gnome-terminal', '-x', 'bash', '-c', 'melt /home/jiceq/Desktop/pelota.mov;bash']
subprocess.call(command6, shell=True, env=os.environ.copy(),stdout=PIPE)

Habitual · 07-24-2015, 01:52 PM

You said gnome terminal runs, but maya fails on

Code:

mlt_repository_init: failed to dlopen /usr/lib64/mlt/libmltavformat.so

so, create a shell script and use
#!/bin/bash
Stick env ($PATH) variables here.
/path/to/melt /home/jiceq/Desktop/pelota.mov

save and exit. chmod etc.
command6 = ['gnome-terminal', '-x', 'bash', '-c', '/home/x/script.sh']
subprocess.call(command6, shell=True, env=os.environ.copy(),stdout=PIPE)

Not to doubt dugan, but is shell=True even necessary if we open/exec/run a terminal emulator that opens a shell already?
Unless this for some visual feedback (cheap debugger?)

Doesn't seem very pythonic to me. But I'm new to the game.

Thanks.

Tinkster · 07-24-2015, 01:54 PM

Moved: This thread is more suitable in <PROGRAMMING> and has been moved accordingly to help your thread/question get the exposure it deserves.

jiceq · 07-27-2015, 03:50 AM

Hi Guys,

Dugan, as far as i can tell since i searched for it on google, subprocess.call admits a string as the commands but will try your point as soon as i can since it seems safer and the right way to do it. I don't have much hope it will work since it's quite the same as the string but will try anyway just in case.

On the other hand my other problem is i dont know what's the configuration the shell loads when i launch it manually hence, i cannot be sure what ENV variables to add to the shell script or even if it is a problem of env variables.

I tried something like:

Code:

!#/bin/sh
source /etc/bashrc
source /etc/profile
melt "#@"

in the melt.sh
and the following:

Code:

command4 = "sh /home/rigging/Desktop/melt.sh /home/rigging/Desktop/pelota.mov"
subprocess.call(command4, shell=True, env=os.environ.copy(),stdout=PIPE)

but didn't work either.

jiceq · 07-27-2015, 09:00 AM

Tried this as said:

Code:

command7 = ['gnome-terminal', '-x', 'bash', '-c', 'melt /home/jiceq/Desktop/pelota.mov;bash']
subprocess.call(command7, shell=False, env=os.environ.copy(),stdout=PIPE)

Had to set "shell=False" otherwise it only launches a terminal and nothing more.

The result is the same as i had with the string command:

Code:

mlt_repository_init: failed to dlopen /usr/lib64/mlt/libmltavformat.so
  (/lib64/libavfilter.so.4: symbol sws_isSupportedEndiannessConversion, version LIBSWSCALE_2 not defined in file libswscale.so.2 with link time reference)

Maybe executing a shell script that previously loads proper configuration is the way to go.... Any ideas on this? I'm using Centos 7. It has to be something wrong with the terminal's config not being the same....

jiceq · 07-28-2015, 05:10 AM

I've discovered something really interesting:

When i launch the terminal through subprocess.call it gives the error i previously posted. But then i tried to call the videoplayer manually in the same terminal and didn't work either, whereas if i open a new terminal it works.

Furthermore, i've discovered that if in that terminal i type "ldconfig" with root privileges and then i call manually de videoplayer.... it works!!!!!

So, my conclusion:

What is more precisely preventing the videoplayer to be launched is that the terminal's config does not recognize the path to the dynamic libraries, rebuilding the ld.so.cache makes it load and recognize the paths which is what ldconfig apparently does. The only problem is that it requires root permissions to write the cache.

So i got a pathway here, i only need to automate it through a script something like:

#!/bin/bash
sudo ldconfig
melt "!@"

and be able to do it without asking for a password. For this ive tried to edit the /etc/sudoers list and add my user but no chance!

You guys certainly know how to do this!! Any help?

jiceq · 07-28-2015, 06:01 AM

guys this is driving me crazy, i think fate doesnt want me to get this through

My Python Script:

Code:

command8 = ['gnome-terminal', '-x', 'bash', '-c', 'sh /home/jiceq/Desktop/melt2.sh /home/jiceq/Desktop/pelota.mov;bash']
call(command8, shell=False, env=os.environ.copy(),stdout=PIPE)

My Sh Script:

Code:

#! /bin/bash

source /home/jiceq/.bashrc
source /home/jiceq/.bash_profile
sudo ldconfig
melt "#@"

The end of my sudoers file without any errors:

Code:

jiceq ALL=(ALL) NOPASSWD:/sbin/ldconfig

Result: Same error!!
But: if i login as root in that shell and run "ldconfig" and then run manually the videoplayer it works!

What's going on here??