Transformer preparations and encoder.

def encode(x, x_space, hparams, name):
  """Transformer preparations and encoder."""
  with tf.variable_scope(name):
    (encoder_input, encoder_self_attention_bias,
     ed) = transformer.transformer_prepare_encoder(x, x_space, hparams)
    encoder_input = tf.nn.dropout(encoder_input, 1.0 - hparams.dropout)
    return transformer.transformer_encoder(
        encoder_input, encoder_self_attention_bias, hparams), ed