I'm trying to run a simple application with Twisted and Qt4, but I get a really strange behavior from my main script. I can't understand if it's a python or a twisted or a Qt4 problem I'm using this reactor: http://twistedmatrix.com/trac/attachment/ticket/1770/qt4reactor.py Now, if I run this: # >>>>>>>>> import qt4reactor import sys from PyQt4 import QtGui from winIum import Window def main(): app = QtGui.QApplication(sys.argv) qt4reactor.install(app) MainWindow = QtGui.QMainWindow() win = Window(MainWindow) MainWindow.show() from twisted.internet import reactor reactor.run() # <<<<<<<< my window shows and run correctly. If I run this: # >>>>>>>>>>>>> import qt4reactor import sys from PyQt4 import QtGui from winIum import Window def creApp(): app = QtGui.QApplication(sys.argv) qt4reactor.install(app) return app def creWin(): MainWindow = QtGui.QMainWindow() win = Window(MainWindow) MainWindow.show() def main(): app = creApp() creWin() from twisted.internet import reactor reactor.run() # <<<<<<<<<<<<< my window doesn't show and the script doesn't stop but remains trapped in some gui loop. What's the problem I can't see?? Thank you in advance for any help. Licia