Custom PointsItemList

I am working on a keypoint regression problem for which I have successfully used the PointsItemList class. However, now I would like to extend it such that each image, in addition to the ImagePoints object, also has an associated category label.

I thought I might be able to implement this just by subclassing PointsItemList and overriding the get(i) method, but not clear as the dependency tree is so huge.

Does anyone have a clue as to how this could be achieved?