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

def _get_cell_type(cell_type):
    """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
    """
    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