PyQt4 Checkbox not responding - OSX

I am getting a really weird issue here. A simple python app with a checkbox once i click on the checkbox (cb) it doesn't change its state and it doesn't change the GUI visualization.

Any ideas ?

Here is my python snippet

a = QApplication(sys.argv)
w = QWidget()
cb = QCheckBox("Auto-Launch", w)
cb.move(220, 110)
cb.stateChanged.connect(handleLaunch)

thank you