code: def _get_cell_type(cell_type):
      
      if isinstance(cell_type, str):
          if cell_type == 'lstm':
              return rnn.LSTMCell
          elif cell_type == 'gru':
              return rnn.GRUCell
          elif cell_type == 'relu_rnn':
              return partial(rnn.RNNCell, activation='relu')
          elif cell_type == 'tanh_rnn':
              return partial(rnn.RNNCell, activation='tanh')
          else:
              raise NotImplementedError
      else:
          return cell_type
docs: Get the object type of the cell by parsing the input
  
      Parameters
      ----------
      cell_type : str or type
  
      Returns
      -------
      cell_constructor: type
          The constructor of the RNNCell