    def _create_placeholders(self):
        """Create all necessary placeholders."""

        self._observations_ph = tf.placeholder(
            tf.float32,
            shape=(None, *self._observation_shape),
            name='observations')

        self._next_observations_ph = tf.placeholder(
            tf.float32,
            shape=(None, *self._observation_shape),
            name='next_observations')

        self._actions_ph = tf.placeholder(
            tf.float32,
            shape=(None, *self._action_shape),
            name='actions')

        self._next_actions_ph = tf.placeholder(
            tf.float32,
            shape=(None, *self._action_shape),
            name='next_actions')

        self._rewards_ph = tf.placeholder(
            tf.float32,
            shape=(None, 1),
            name='rewards')

        self._terminals_ph = tf.placeholder(
            tf.float32,
            shape=(None, 1),
            name='terminals')
Create all necessary placeholders.
softlearning/algorithms/sql.py