class_docstr: Run a pre-trained bidirectional language model, outputing the activations at each
  layer for weighting together into an ELMo representation (with
  ``allennlp.modules.seq2seq_encoders.Elmo``).  This is a lower level class, useful
  for advanced uses, but most users should use ``allennlp.modules.seq2seq_encoders.Elmo``
  directly.
  
  Parameters
  ----------
  options_file : ``str``
      ELMo JSON options file
  weight_file : ``str``
      ELMo hdf5 weight file
  requires_grad: ``bool``, optional
      If True, compute gradient of ELMo parameters for fine tuning.
  vocab_to_cache : ``List[str]``, optional, (default = 0.5).
      A list of words to pre-compute and cache character convolutions
      for. If you use this option, _ElmoBiLm expects that you pass word
      indices of shape (batch_size, timesteps) to forward, instead
      of character indices. If you use this option and pass a word which
      wasn't pre-cached, this will break.
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code: def get_output_dim(self):
      return 2 * self._token_embedder.get_output_dim()
  
imports: from __future__ import with_statement
  from __future__ import absolute_import
  import json
  import logging
  import warnings
  import torch
  from torch.nn.modules import Dropout
  import numpy
  from io import open
  from allennlp.common.file_utils import cached_path
  from allennlp.common.checks import ConfigurationError
  from allennlp.common import Params
  from allennlp.common.util import lazy_groups_of
  from allennlp.modules.elmo_lstm import ElmoLstm
  from allennlp.modules.highway import Highway
  from allennlp.modules.scalar_mix import ScalarMix
  from allennlp.nn.util import remove_sentence_boundaries, add_sentence_boundary_token_ids, get_device_of
  from allennlp.data.token_indexers.elmo_indexer import ELMoCharacterMapper, ELMoTokenCharactersIndexer
  from allennlp.data.dataset import Batch
  from allennlp.data import Token, Vocabulary, Instance
  from allennlp.data.fields import TextField
label_desc: Use image node_id 2 for calling the _ElmoBiLm obj's underlying member method code with example usage: obj.get_output_dim() and returns: unknown