Launch just one instance of a Qt application

Problem
I have a Qt application that I only want to run in one instance. If I forget that it’s launched and I start it again, I want the system to put the focus on the already running instance.

Solution
For more details, see this post where the used Unix commands are explained.

#!/usr/bin/env python

"""
Launch just one instance of an application.

If the application is running, the focus is put on its window.

Requires the xdotool package (sudo apt-get install xdotool).
Tested under Ubuntu GNU/Linux 12.10.

Author: Laszlo Szathmary (jabba.laci@gmail.com), 2013
"""

__author__ = 'Jabba Laci'
__appname__ = "The One and Only"
__version__ = "0.1"

import os
import sys
from PySide.QtGui import *
from PySide.QtCore import *
from subprocess import Popen, PIPE, STDOUT
import shlex


def get_simple_cmd_output(cmd, stderr=STDOUT):
    """Execute a simple external command and get its output.

    The command contains no pipes. Error messages are
    redirected to the standard output by default.
    """
    args = shlex.split(cmd)
    return Popen(args, stdout=PIPE, stderr=stderr).communicate()[0]


class OneDialog(QDialog):
    def __init__(self, parent=None):
        super(OneDialog, self).__init__(parent)
        self.setWindowTitle("{} {}".format(__appname__, __version__))
        self.resize(300,150)

####################

if __name__ == "__main__":
    wid = get_simple_cmd_output('xdotool search --name "{n}"'.format(n=__appname__)).strip()
    if wid:
        os.system('xdotool windowactivate {}'.format(wid))
    else:
        app = QApplication(sys.argv)
        form = OneDialog()
        form.show()
        app.exec_()

If you have a better solution, let me know.

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