Python subprocess.Popen() questions

Coding
1

Hey guys,

I’m trying to use subprocess to gather some information from one of our tools that needs to be run via cmd line within our shell.

I am running subprocess.Popen() from within a script called within Maya to do this.

Maya is running within our shell, that is setup via batch at Maya launch.



gameRoot=os.environ.get("GAME_ROOT") + '\	ools\\options'
_cmd=[r'python', 'import os', 'os.environ.copy()']
		
task = subprocess.Popen(_cmd, cwd=gameRoot, stdout=subprocess.PIPE) #shell=True,
task.wait()

I am finding as soon as I introduce the subprocess.PIPE to the mix I get a funky crash. Obviously I need the Pipe to retrieve the data I want.

Error: (6, ‘The handle is invalid’)

Traceback (most recent call last):

File “<maya console>”, line 1, in <module>

File “…\maya\2009\python\ssgtools\utils\ssgSubProc.py”, line 10, in ssgSubProcGetEnv

task = subprocess.Popen(_cmd, cwd=gameRoot, stdout=subprocess.PIPE) #shell=True,

File “C:\Program Files (x86)\Autodesk\Maya2009\bin\python25.zip\subprocess.py”, line 586, in init

errread, errwrite) = self._get_handles(stdin, stdout, stderr)

File “C:\Program Files (x86)\Autodesk\Maya2009\bin\python25.zip\subprocess.py”, line 699, in _get_handles

p2cread = self._make_inheritable(p2cread)

File “C:\Program Files (x86)\Autodesk\Maya2009\bin\python25.zip\subprocess.py”, line 744, in _make_inheritable

DUPLICATE_SAME_ACCESS)

WindowsError: (6, ‘The handle is invalid’)

My solution is to write the data to a file on disk as I have this option with the exe I need to use, then read that files contents in and use that, but it kinda defeats the point of being able to run a sub process and create a temp file using temp file then pull the data from that container.

any ideas? Its driving me nuts…

2

Try capturing both stdout and stderr. Also try communicate:

stdout, stderr = subprocess.Popen(_cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
3

You cannot use PIPE’s from within Maya. It sucks so bad. It is a known python bug when using Popen through some GUI apps.

So, yes, figure out some workaround like you have.

4

Use sockets to communicate with your tools, you can write in any language then.

5 
You cannot use PIPE's from within Maya. It sucks so bad. It is a known python bug when using Popen through some GUI apps.

We do it a fair bit. Mind you, we are using Maya 2009 python still, perhaps something broke down the line.

6

Autodesk modifies the standard subprocess module, and I had run into an issue in Maya 2011 where that would cause pipes to fail (Non file-like object error). Luckily they include the originals in the python26.zip file. It’s called: subprocess_original, just import it instead of subprocess. (Although I don’t think this is your issue here).

Also as Rob mentioned, typically the DUPLICATE_SAME_ACCESS error is related to only passing a PIPE as either stdin or stdout but not both. Try using them as both even if you don’t need it.

7

Workaround on Windows:


# command_string is my command with any arguments
windows_wrapper_string = 'start ' + command_string
os.system( windows_wrapper_string )