code: def _post_build(self):
      # DND gradients
      self.dnd_embeddings_grad = tf.gradients(
          self.loss[0], self.dnd_embeddings
      )
      self.dnd_values_grad = tf.gradients(self.loss[0], self.dnd_values)
  
file_path: coach/rl_coach/architectures/tensorflow_components/heads/dnd_q_head.py
imports: import tensorflow
  from rl_coach.architectures.tensorflow_components.layers import Dense
  from rl_coach.architectures.tensorflow_components.heads.q_head import QHead
  from rl_coach.base_parameters import AgentParameters
  from rl_coach.memories.non_episodic import differentiable_neural_dictionary
  from rl_coach.spaces import SpacesDefinition
label_desc: Use image node_id 4 for calling the DNDQHead obj's underlying member method code with example usage: obj._post_build() without return types