[Tutor] os.system vs subprocess.Popen args problems

[Oscar Benjamin]

On 4 September 2013 11:11, eryksun <eryksun at gmail.com> wrote:
> On Wed, Sep 4, 2013 at 5:14 AM, learner404 <learner404 at gmail.com> wrote:
>>
>> Yes, this worked :)
>>
>> subprocess.Popen(["ffmpeg","-f","dshow","-i","video="+videoinputName,"-f",
>> "dshow","-i","audio="+audioinputName,"-q","5","%s"%videoFileOutput],
>> shell=True)

You should use subprocess.check_call() rather than subprocess.Popen.
subprocess.check_call() waits for the command to complete and detects
when an error has occurred in the child process and turns it into a
Python error which is normally what you want to happen before any
subsequent code runs.

>From the subprocess docs:
"The recommended approach to invoking subprocesses is to use the
following convenience functions for all use cases they can handle. For
more advanced use cases, the underlying Popen interface can be used
directly."
http://docs.python.org/2/library/subprocess.html#using-the-subprocess-module

I'm pretty sure that your problem does not come under the "more
advanced" use cases of subprocess.

> Using shell=True also sets startupinfo to hide the window. If that's
> the only reason you're using the shell, you may as well cut out the
> middleman (and potential security hole). Set startupinfo=si, where si
> is defined like this:

I think it should just be possible to use shell=False here.

>     si = subprocess.STARTUPINFO()
>     si.dwFlags |= subprocess.STARTF_USESHOWWINDOW
>     si.wShowWindow = subprocess.SW_HIDE

Do these statements modify module-level state? Or do you need to pass
startupinfo=si when calling Popen?


Oscar