class_docstr: Base class inherited by all RNN decoder classes.
  See :class:`~texar.tf.modules.BasicRNNDecoder` for the argumenrts.
  
  See :meth:`_build` for the inputs and outputs of RNN decoders in general.
  
  .. document private functions
  .. automethod:: _build
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docstr: Returns a dictionary of hyperparameters with default values.
  
  The hyperparameters are the same as in
  :meth:`~texar.tf.modules.BasicRNNDecoder.default_hparams` of
  :class:`~texar.tf.modules.BasicRNNDecoder`, except that the default
  "name" here is "rnn_decoder".
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code: def default_hparams():
      """Returns a dictionary of hyperparameters with default values.
  
      The hyperparameters are the same as in
      :meth:`~texar.tf.modules.BasicRNNDecoder.default_hparams` of
      :class:`~texar.tf.modules.BasicRNNDecoder`, except that the default
      "name" here is "rnn_decoder".
      """
      return {
          "rnn_cell": layers.default_rnn_cell_hparams(),
          "helper_train": rnn_decoder_helpers.default_helper_train_hparams(),
          "helper_infer": rnn_decoder_helpers.default_helper_infer_hparams(),
          "max_decoding_length_train": None,
          "max_decoding_length_infer": None,
          "name": "rnn_decoder",
          "output_layer_bias": True,
      }
  
imports: import copy
  import tensorflow
  from tensorflow.contrib.seq2seq import Decoder
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.util import nest
  from texar.tf.core import layers
  from texar.tf.utils import utils
  from texar.tf.utils.mode import is_train_mode, is_train_mode_py
  from texar.tf.modules.decoders.dynamic_decode import dynamic_decode
  from texar.tf.module_base import ModuleBase
  from texar.tf.modules.decoders import rnn_decoder_helpers
  from texar.tf.utils.dtypes import is_callable
  from texar.tf.utils.shapes import shape_list
  from texar.tf.modules.decoders import tf_helpers
label_desc: Use image node_id 2 for calling the RNNDecoderBase obj's underlying member method code with example usage: obj.default_hparams() and returns: dict