[PyQt] Errors when quitting event loop

[Bart Kroon]

When the Python interpreter is shutting down all objects are set to None. When 
another thread is then accessing the QObject subclass it finds None and gives 
an error.

You say you are not spawning QThreads but are you using Python threads?

These errors are mostly harmless but if you must get rid of them make sure all 
threads are joined before calling sys.exit().