CvSize does not exist?
Perhaps the documentation is wrong and you have to use cv.cvSize instead of cv.CvSize ?
Also, do a dir(cv) to find out the methods available to you.
I have installed the official python bindings for OpenCv and I am implementing some standard textbook functions just to get used to the python syntax.  I have run into the problem, however, that CvSize does not actually exist, even though it is documented on the site...  
The simple function: blah = cv.CvSize(inp.width/2, inp.height/2) yields the error 'module' object has no attribute 'CvSize'.  I have imported with 'import cv'.
Is there an equivalent structure?  Do I need something more?  Thanks.