python - PyQt drops all of signals and slots after using chained invoke like pyObj.setupUi(parent) -

all of singals (for example textchanged in below codes) dropped , printdummy function silented once used dummywidget().setupui(mainwin), working when used dw = dummywidget(); dw.setupui(main). didn't see specific difference in python's syntax. can share comment?

class dummywidget(object):     def setupui(self, parent=none):         assert parent not none         self.parent = parent         parent.resize(480, 320)         self.dummy = qtgui.qlineedit(parent)         # parent.setcentralwidget(self.dummy)         self.dummy.textchanged.connect(self.printdummy)         qtgui.qapplication.processevents()      def printdummy(self):         print "dummy in class"   if __name__ == "__main__":     import sys      def printdummy(*args):         print "dummy"      app = qtgui.qapplication(sys.argv)     # mainwin = mainwindow()     # edit = qtgui.qlineedit()     # edit.textchanged.connect(printdummy)     # mainwin.setcentralwidget(edit)     mainwin = qtgui.qdialog()     # dummywidget().setupui(mainwin)     dw = dummywidget()     dw.setupui(mainwin)     mainwin.show()     # mainwin.open()     sys.exit(app.exec_()) 

if don't keep reference instance of dummywidget garbage collected, hence slot no longer exist.

if dummywidget.setupui(parent) cannot store reference (this line gives return value of setupui none).