def sess(self) -> "tf.python.client.session.Session":
        """
        Get current TensorFlow session.

        :return: The current TensorFlow session.
        """
        if self._sess is not None:
            return self._sess

        raise NotImplementedError("A valid TensorFlow session is not available.")

        Get current TensorFlow session.

        :return: The current TensorFlow session.
        
art/estimators/tensorflow.py