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My code is just over 400 lines long right now and I would prefer to not be given the answer to this but rather some suggestions of what could be wrong. In my program I start a sub process with:

#out_select is a variable that defaults to the AD9850 control program
#and is switched to the sinetable program with the valve_select command.
subprocess.call(out_select, shell=True)
#The following lines are used to find the PID of the program used for output
#and save it for the stop command to kill that PID.
sp = subprocess.Popen(['python',out_select])
end_sine = int(sp.pid)-1
print end_sine
#end = str(end_sine)

This is started with a tkinter button command. The program does start in the background but I . I receive the following error message in my LXTerminal when I initiate the command ( by clicking the button):

python: can't open file 'python DACscrap.py &': [Errno 2] No such file or directory

or depending on the command out_select:

python: can't open file 'sudo python AD9850_GUI.py &': [Errno 2] No such file or directory

Both programs do run fine as verified with an oscilloscope and I am able to return to the program and use the other button widgets. The hangup is that there is a graph in the program and I can't values being sent from an arduino over the USB port. It's not the arduino because the graph would graph a value of zero. Any suggestions on where the problem might be? If not with the few lines here then could I be doing something elsewhere?

J.Doe
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1 Answers1

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The error message means that python executable that you are trying to start using sp = subprocess.Popen(['python',out_select]) can't find the filename that contains in out_select variable (and indeed, it is very unlikely that you have a Python script stored in a file named: 'python DACscrap.py &' literally).

Try to familiarize yourself with running external processes:

  • don't use shell=True, to run a single command. Pass a list instead
  • don't use & (Popen does not wait for the command to exit)

e.g., instead of call("cmd 'arg 1' arg2 &", shell=True), use:

p = Popen(['cmd',  'arg 1',  'arg2'])
# ... do something else
p.wait()

It might be more convenient to import Python modules and call the corresponding functions instead of running the Python files as scripts using subprocess. See Call python script with input with in a python script using subprocess

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jfs
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