From Forum Nokia Wiki

This method is used for debugging standalone applications in PyS60

try:
    # Actual program is here.
    1 / 0
except:
    import sys
    import traceback
    import e32
    import appuifw
    appuifw.app.screen="normal"              # Restore screen to normal size.
    appuifw.app.focus=None                   # Disable focus callback.
    body=appuifw.Text()
    appuifw.app.body=body                    # Create and use a text control.
    applock=e32.Ao_lock()
    def quit():applock.signal()
    appuifw.app.exit_key_handler=quit        # Override softkey handler.
    appuifw.app.menu=[(u"Exit", quit)]       # Override application menu.
    body.set(unicode("\n".join(traceback.format_exception(*sys.exc_info()))))
    applock.wait()                           # Wait for exit key to be pressed.
    appuifw.app.set_exit()

More methods for debugging standalone applications in Python can be found in the article Python debugging techniques.