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.
PythonQt only creates Python wrappers for C++ instances that are exposed to Python.
So if you do not expose millions of C++ instances to Python at the same time,
it will scale nicely and create wrappers only for the exposed objects.
These wrappers are deleted when they go out of scope in Python, so this should scale as well.
The best way to wrap a C++ object is to register a decorator QObject derived class for each C++ class, this allows to register many classes without actually creating/evaluating the decorators until a class of that type becomes visible to Python.
Have a look at the Qt wrappers, e.g. PythonQtWrapper_QImage, to see how such a decorator looks like and how it is registered.
scalability of pythonqt for millions of objects