def _evaluate(
        sess,
        feed_dict,
        eval_op):
    """ Evaluates one batch of feeding data.

    Args:
        sess: `tf.Session`.
        feed_dict: A dictionary of feeding data.
        eval_op: Tensorflow operation.

    Returns: Results of `eval_op`.

    """
    return sess.run(eval_op, feed_dict=feed_dict)