[PySide] using QProcess to run python function

Fri Jan 24 05:30:08 CET 2014

On Thu, Jan 23, 2014 at 10:39 PM, Frank Rueter | OHUfx <frank at ohufx.com>wrote:

>  I might have lead you on a wild goose chase:
>
> I have working python code that calls external process (using
> subprocess.Popen) and now I am writing a UI for it.
>
> To get started I wrote a simple UI that connected to one of those external
> programs directly to establish the frame work for the new code and figure
> out how to properly handle the external programs stdout and stderr, be able
> to display things and cancel it from within my UI.
> After getting all that to work I thought all I have to do is connect to my
> actual python code rather than directly to the external program, and that
> is where I assumed QProcess to be able to do this, when instead I shuold
> simlpy switch to use QThread and reire that to give me access to stdout, be
> able to cancel it etc.
> So what I am trying to do is simply this:
>
> PySide UI --- calls --> pure python --- calls --> pure python --- calls--> external program
>
> With the stdout of external program and the pure python apps being piped
> into the PySide UI for processing.
>
I assume each of these is in its own process:

|process|    | process |    | process |    |   process    |
PySide UI -> pure Python -> pure Python -> external program

Since creating processes is somewhat expensive, have you considered the
following?

|              process                |    |   process    |
PySide UI -> pure Python -> pure Python -> external program
          ^              ^              ^
       imports        imports       subprocess

This would be ideal if import is a possibility. Apologies for the crude
drawings :)

>
>
> Sorry if I wasted your time :/
>

>
>
> frank
>
>
>
>
> On 24/01/14 16:22, Sean Fisk wrote:
>
>  Are you wanting to use QProcess or QThread because your GUI is blocked
> (aka frozen, not responding)?
>
>
>  --
> Sean Fisk
>
>
> On Thu, Jan 23, 2014 at 10:06 PM, Frank Rueter | OHUfx <frank at ohufx.com>wrote:
>
>>  Actually, it's dawning on me that QProcess may be the wrong thing to use
>> here, I guess I should consider using QThread instead, seeing all the code
>> I need to run is Python anyway!?
>> I was just experimented with QProcess running the external programs
>> directly for testing so I kinda got stuck in thinking this is the way to go
>> (since I got it all wired up to my UI already).
>>
>>
>>
>>
>>
>> On 24/01/14 15:42, Frank Rueter | OHUfx wrote:
>>
>> Thanks Sean and Ryan,
>>
>> I'm still not quite clear on how this ties into QProcess.start()
>> I do have a if __name__ ... block in the script in question.
>> An example would certainly be awesome, but if it's less hassle,
>> explaining how your and Ryan's advise helps use QProcess on a python module
>> might already suffice. Maybe a simlpe example says it all though?!
>> I'm not using python 3 btw
>>
>> Thanks guys for your help!!
>>
>> frank
>>
>> On 24/01/14 15:33, Sean Fisk wrote:
>>
>>  Hi Frank,
>>
>> You should definitely avoid calling Python as a subprocess if you can. As
>> far as Ryan’s example, I agree with the if __name__... but I think that
>> using the imp module is a bit overkill. I would recommend using
>> Setuptool’s entry_points keyword<http://pythonhosted.org/setuptools/setuptools.html#automatic-script-creation>.
>> Or distutils’ scripts keyword<http://docs.python.org/2/distutils/setupscript.html#installing-scripts>,
>> if you must.
>>
>> An example of a well-known Python package which does this is Pygments<https://bitbucket.org/birkenfeld/pygments-main>,
>> which has a large “library” component but also comes with the pygmentizecommand-line script. The Pygments codebase is pretty large, so if you would
>> like me to whip up a simpler example I’d be glad to do so.
>>
>> Cheers,
>>   --
>> Sean Fisk
>>
>>
>> On Thu, Jan 23, 2014 at 9:17 PM, Frank Rueter | OHUfx <frank at ohufx.com>wrote:
>>
>>>  Sorry if I'm being thick, but I'm not quite understanding how this
>>> helps to connect a python function to qprocess?! All your code does is
>>> execute the script, right?!
>>> I can already call myscript.main() straight up, but maybe I'm missing
>>> the point as I'm unfamiliar with the imp module.
>>>
>>> Let me elaborate a little bit more:
>>> myscript.main() calls a bunch of other python scripts that (directly or
>>> through other scripts again) execute external programs to do some
>>> conversion work. Those external programs spit out their progress to stdout
>>> which I can see fine when I run myscript.main() manually in a python
>>> terminal.
>>>
>>> Now I need run myscript.main() via QProcess and grab stdout to do be
>>> able to show a progress bar as well as show stdout and stderr in a debug
>>> window inside my QT code.
>>>
>>>
>>> Cheers,
>>> frank
>>>
>>>
>>>
>>>
>>> On 24/01/14 14:58, Ryan Gonzalez wrote:
>>>
>>> If you put an "if __name__ == '__main__'" and a main functions, you
>>> could always import the script from the GUI frontend. Example:
>>>
>>>  myscript.py
>>>
>>>  def main(argv):
>>>     do_cool_stuff()
>>>     return 0
>>>
>>>  if __name__ == '__main__':
>>>     sys.exit(main(sys.argv))
>>>
>>>  mygui.py(Python 2):
>>>
>>>  import imp
>>>
>>>  ...
>>>
>>>  main = imp.load_module('myscript', *imp.find_module('myscript'))
>>>
>>>  main.main(my_argv)
>>>
>>>  mygui.py(Python 3):
>>>
>>>  import importlib.machinery
>>>
>>>  main = importlib.machinery.SourceFileLoader('myscript',
>>> 'myscript.py').load_module('myscript')
>>>
>>>  main.main(my_argv)
>>>
>>>
>>> On Thu, Jan 23, 2014 at 7:48 PM, Frank Rueter | OHUfx <frank at ohufx.com>wrote:
>>>
>>>> Hi all,
>>>>
>>>> I got a little code design question:
>>>>
>>>> I have a python script that does a lot of file
>>>> processing/converting/uploading etc and I'd like to write a decent
>>>> interface for it now.
>>>> The main goal is to be able to show the user detailed info about the
>>>> current step and progress as well as clean up properly in case the whole
>>>> thing is cancelled.
>>>>
>>>> My existing python code needs to stay independent of QT so any
>>>> application that supports python can use it.
>>>> I am wondering now how to best connect the python script and the PySide
>>>> code. Should I just run the script as an argument to the python
>>>> interpreter like I would with any other program? E.g.:
>>>>
>>>> process = QtCore.QProcess(self)
>>>> process.start(<path_to_python>, <path_to_python_script>)
>>>>
>>>> As simple as this seems, it feels odd to use python to call itself as an
>>>> external program.
>>>>
>>>>
>>>> I'm happy to go that way but am curious how others are doing this?!
>>>>
>>>> Cheers,
>>>> frank
>>>>
>>>> _______________________________________________
>>>> PySide mailing list
>>>> PySide at qt-project.org
>>>> http://lists.qt-project.org/mailman/listinfo/pyside
>>>>
>>>
>>>
>>>
>>>  --
>>> Ryan
>>> If anybody ever asks me why I prefer C++ to C, my answer will be simple:
>>> "It's becauseslejfp23(@#Q*(E*EIdc-SEGFAULT. Wait, I don't think that was
>>> nul-terminated."
>>>
>>>
>>>
>>> _______________________________________________
>>> PySide mailing list
>>> PySide at qt-project.org
>>> http://lists.qt-project.org/mailman/listinfo/pyside
>>>
>>>
>>
>>
>>
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