pyqt4 - simple IPython example raises exception on sys.exit() -

i'm doing simple pyside (and pyqt) tutorials in ipython. 1 tutorial creates window sliders demonstrate slots , signals.

when close window of running demo application, see error:

an exception has occurred, use %tb see full traceback. systemexit: 0 exit: use 'exit', 'quit', or ctrl-d. 

so run %tb , this:

systemexit                                traceback (most recent call last) /workspaces/scratch/<ipython-input-1-88966dcfb499> in <module>()      33       34 if __name__ == "__main__": ---> 35     main()  /workspaces/scratch/<ipython-input-1-88966dcfb499> in main()      29         w.show()      30         app.exec_() ---> 31         sys.exit(0)      32       33   systemexit: 0 

if try execute code again, this:

runtimeerror: qapplication instance exists. 

in case helps, here code:

from pyside.qtcore import * pyside.qtgui import * import sys  class mywindow(qwidget):     def __init__(self):         qwidget.__init__(self, none)          vbox = qvboxlayout(self)          self.slider1 = qslider(qt.horizontal)         self.slider1.setrange(0, 99)         self.slider1.setvalue(0)         vbox.addwidget(self.slider1)          self.slider2 = qslider(qt.horizontal)         self.slider2.setrange(0, 99)         self.slider2.setvalue(99)         vbox.addwidget(self.slider2)          self.slider1.valuechanged.connect(self.slider2changed)      def slider2changed(self, position):         self.slider2.setvalue(self.slider2.maximum() - position)  def main():         app = qapplication(sys.argv)         w = mywindow()         w.show()         app.exec_()         sys.exit(0)  if __name__ == "__main__":     main() 

i not have errors when running code using python:

python myexample.py 

this error happens when run code in ipython (including notebook or qtconsole or regular ipython terminal).

update: main problem cannot run application again , easily. if try run code again, this:

runtimeerror: qapplication instance exists. 

that kills fast, interactive nature of ipython :(

what need cause qapplication deleted later in:

app = qapplication(sys.argv) app.abouttoquit.connect(app.deletelater) 

using code can rerun application many times want in ipython, or anywhere else , every time close qt application, object deleted in python.