[PySide] IPython Mac 10.7 QApplication instance already exists

Nathan Smith nathanjsmith at gmail.com
Wed May 23 23:03:56 CEST 2012

Hi Jason,

PySide only supports creating a single persistent instance of QApplication.
This singleton exists forever and cannot be deleted.  If you have a
function that tries to create a QApplication, then I recommend placing that
creation inside of a try/except block:

  app = QtGui.QApplication(sys.argv)
except RuntimeError:
  app = QtCore.QCoreApplication.instance()

This will either create a new QApplication instance if one does not exist,
or return the current QApplication instance if one already does exist.


On Wed, May 23, 2012 at 3:21 PM, Jason Augustyn <js.augustyn at gmail.com>wrote:

> Hi all, I am new to using PySide and have been working through the novice
> tutorials, which are great. One problem - I cannot re-run a script without
> exiting the Python shell altogether. Re-running gives the RuntimeError: A
> QApplication instance already exists.
> I have searched for a solution and found an old bug tracker ticket from
> someone with a similar problem. The suggested solution was to upgrade to
> PySide 1.0.4 and the ticket was marked as invalid. Obviously that doesn;t
> work, as I'm running the newest version of PySide and still have the
> problem. Any suggestions? I am using IPython on a Mac OSX 10.7.
> Thanks!
> Jason
> _______________________________________________
> PySide mailing list
> PySide at qt-project.org
> http://lists.qt-project.org/mailman/listinfo/pyside
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