'Runs one step of inference.
Args:
sess: TensorFlow Session object.
input_feed: A numpy array of shape [batch_size].
state_feed: A numpy array of shape [batch_size, state_size].
Returns:
softmax_output: A numpy array of shape [batch_size, vocab_size].
new_state: A numpy array of shape [batch_size, state_size].
metadata: Optional. If not None, a string containing metadata about the
current inference step (e.g. serialized numpy array containing
activations from a particular model layer.).'

def inference_step(self, sess, input_feed, state_feed):

    tf.logging.fatal('Please    implement    inference_step    in    subclass')
