'Evaluates and accumulates evaluation metric on outputs of the last forward computation.
Subclass should override this method if needed.
Parameters
eval_metric : EvalMetric
labels : list of NDArray
Typically ``data_batch.label``.'

def update_metric(self, eval_metric, labels):

    if (self._label_shapes is None):
        return
    eval_metric.update(labels, self.get_outputs())
