Python and Glade: window not showing

[Sven Arduwie]

Can anyone help a python newbie and tell me why the simple window I
created in Glade is not showing?

This is the XML generated by Glade 3:
<?xml version="1.0"?>
<interface>
  <requires lib="gtk+" version="2.16"/>
  <!-- interface-naming-policy project-wide -->
  <object class="GtkWindow" id="helloWorld">
    <property name="visible">True</property>
    <signal name="destroy" handler="on_helloWorld_destroy"/>
    <child>
      <placeholder/>
    </child>
  </object>
</interface>

And this is the Python code:
#!/usr/bin/env python

import pygtk
pygtk.require("2.0")
import gtk

class HelloWorld(object):
	def getWindow(self):
		return self.window

	def setWindow(self, window):
		self.window = window

	window = property(getWindow, setWindow)

	def __init__(self):
		builder = gtk.Builder()
		builder.add_from_file("helloWorld.glade")
		builder.connect_signals({"on_helloWorld_destroy" :
self.onHelloWorldDestroy})
		self.window = builder.get_object("helloWorld")
		self.window.show()

	def onHelloWorldDestroy(self):
		pass

I ran this in a terminal on Ubuntu 9.04 like this:
sven at Dell:~$ cd ./gvfs/python\ on\ sven/
sven at Dell:~/gvfs/python on sven$ python ./helloWorld.py
sven at Dell:~/gvfs/python on sven$