Python subprocess.call/Popen/系统问题

Question

I am starting a subprocess by different ways - subprocess.call, Popen, os.system.

For example:

subprocess.call('wine application.exe', shell=True)

But python starts 2 processes:

/bin/sh -c wine application.exe application.exe

When I am starting this application manually by calling in console window wine application.exe I see only application.exe instance in ps ax .

Is it normal? My guess is that is ok because it is subprocess and it's parent waits for child finish. BUT, why this behavior not the same as I'd launched application from console? Where in this case parent hides?

Update: I've thought hard and understood that this is really parent process. If I will launch application from python with: subprocess.call('wine application.exe &', shell=True) it will have same behavior as in shell(because shell is true ). So in this case it will be only one instance - the one you called by this subprocess call.

But anyway I still don't understand why there is 2 processes instead of simply one. Invoker - okay, but where second process came from? Why it doesn't work with 1 process?

Answer 1

When you start an application with shell=True, python starts a shell and the shell starts the program. That's why you see two programs. If you run it like

subprocess.call(['wine', 'application.exe'])

you will only see one.

When you ran it from the command line, you were already in the shell so you only saw 1.

Update

When you ran subprocess.call('wine application.exe &', shell=True) , python executed a shell which executed wine. Since you added &, the shell backgrounded wine and exited. While this may be what you want, the potential downsides are that python doesn't wait for the process to complete and there will be a zombie process left over when your program exits.