Well, I still don't really agree with it. About efficiency, calling SG_REF and SG_UNREF compared to the rest of the stuff you do in the class is negligible. get_labels and set_labels are just the standard getter and setter. Recall also that in some conversation we had a the beginning, Patrick suggested that the labels and the features should not be inside the model, but just in the machine.

That said, keep it this way if you prefer. It is not a so important detail.