I was thinking about adding pythonqt to my application for writing plugins.  My application is in C++ and already uses the Qt framework.  The pythonqt option seems like a natural fit for adding GUI components, but I'm concerned about how well the program will scale if I expose an class with millions of instances.  It will not be uncommon to have something like a million of a certain type of object in memory and I wanted to make sure pythonqt would be able to expose these objects without making them QObjects.  It may be fine, I guess, but before I started, I was wondering if exposing such a large number of classes would be practical using pythonqt and if anyone had any experience with scaling it this much.  
From this link (http://pythonqt.sourceforge.net/Developer.html), it seems the decorators actually only load them into python/Qt on request.  I just don't want an even bigger memory footprint of Qt trying to keep track of these millions of objects for no reason.
I haven't done much with it but it almost sounds like you should at least look at QtQuick/QML layer. It is hard to tell from your description what is going on but QML is a way to write Qt GUIs without doing any C++ coding. It build on the already exisiting and well working Qt/JavaScript Implementation and Bridge. 
As for exposing instances of classes to a scripting language, that would usually depend on the implementation of the bridge. While there is usually some code involved you might not incur that per instance, or it might be lazily instantiated to a point where you will only have much less than the millions of wrapped instances than the originals that you are holding in memory.
scalability of pythonqt for millions of objects