Convert Y to t-length list of probabilistic labels if necessary

def _preprocess_Y(self, Y, k=None):
        """Convert Y to t-length list of probabilistic labels if necessary"""
        # If not a list, convert to a singleton list
        if not isinstance(Y, list):
            if self.t != 1:
                msg = "For t > 1, Y must be a list of n-dim or [n, K_t] tensors"
                raise ValueError(msg)
            Y = [Y]

        if not len(Y) == self.t:
            msg = f"Expected Y to be a t-length list (t={self.t}), not {len(Y)}"
            raise ValueError(msg)

        return [EndModel._preprocess_Y(self, Y_t, self.K[t]) for t, Y_t in enumerate(Y)]