Simple shapes Node-Can Python do this?

I want to make simple shapes for masks or mattes in composite nodes. As there is no node for that (you must build a scene and shoot the shape) could I use python to make such a thing?

I would like to specify a basic shape, square or circle, then animate it’s xy scale and centre position. It would have to take the pixel size of the image it was overlaying though.

Is this still outside of Pythons access in Blender?