I am writing a wxPython application that remains open after closing all of its windows - so you can still drag & drop new files onto the OSX dock icon (I do this with myApp.SetExitOnFrameDelete(False)).
Unfortunately if I close all the windows, the OSX menubar will only contain a "Help" menu. I would like to add at least a File/Open menu item, or just keep the menubar of the main window. Is this somehow possible in wxPython?
In fact, I would be happy with a non-wxPython hack as well (for example, setting the menu in pyobjc, but running the rest of the GUI in wxPython). wxPython development in OSX is such a hack anyway ;)
UPDATE: I managed to solve this problem using the tip from Lyndsey Ferguson. Here's what I have done:

On startup I create a window which I show and hide immediately. I set its position to (-10000,-10000) so that it does not flicker on the screen (aargh, what a dirty hack!)
I create an empty EVT_CLOSE event handler in that window so that it cannot be closed.
It seems that destroying a window resets the OSX menu, but hiding does not... So when the last window is closed, I need to show and hide this window again (hiding is necessary so that the user cannot switch to this window using the Window menu or Cmd-`)

Yeah, this is really ugly... I will be very grateful if someone comes up with a prettier solution.
UPDATE 2: Actually it can be solved in a much easier way: if we do not close the last window, only hide it. And ensure that it does not respond to menu events anymore.
Can you create a hidden window that is offscreen somewhere? It is a hack, but I remember having to do a lot of hacks to make my wxPython-based application work correctly on Mac OS X.
Note:You'll have to disable the close button and set up that hidden window so that it doesn't show up in the Window menu.
Aside:Have you considered factoring out your GUI portion of your Python application and using PyObjC on Mac OS X? You'll get more native behaviours...
How to change the OSX menubar in wxPython without any opened window?