Really strange behavior

[IloChab]

Sorry I wasn't able to be more specific on my topic but I really do not
know how to classify my  problem, I mean that I can't understand if it's 
a python
or a twisted
or a Qt4
problem
I'm trying to run a simple application with Twisted and Qt4. 
To do this I downloaded this:
    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)
    retrun 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