def show_metrics(step_value, metric_values, loss_value=None):
  print('{}: {}nominal accuracy = {:.2f}%, '
        'verified = {:.2f}%, attack = {:.2f}%'.format(
            step_value,
            'loss = {}, '.format(loss_value) if loss_value is not None else '',
            metric_values.nominal_accuracy * 100.,
            metric_values.verified_accuracy * 100.,
            metric_values.attack_accuracy * 100.))