code: def get_rnn_cell_trainable_variables(cell):
      """Returns the list of trainable variables of an RNN cell.
  
      Args:
          cell: an instance of :tf_main:`RNNCell <nn/rnn_cell/RNNCell>`.
  
      Returns:
          list: trainable variables of the cell.
      """
      cell_ = cell
      while True:
          try:
              return cell_.trainable_variables
          except AttributeError:
              # Cell wrappers (e.g., `DropoutWrapper`) cannot directly access to
              # `trainable_variables` as they don't initialize superclass
              # (tf==v1.3). So try to access through the cell in the wrapper.
              cell_ = cell._cell
  
imports: import copy
  import tensorflow
  import tensorflow.contrib.rnn
  from texar.tf.hyperparams import HParams
  from texar.tf.utils import utils
  from texar.tf.utils.dtypes import is_str
  from texar.tf.utils.variables import add_variable
  from texar.tf.utils.mode import is_train_mode, switch_dropout
label_desc: Use image node_id 3 for calling a global function with example usage: get_rnn_cell_trainable_variables(cell) and returns: cell_