code: def predict(self, obs):  # 选择最优动作
      obs = np.expand_dims(obs, axis=0)
      pred_Q = self.fluid_executor.run(
          self.pred_program,
          feed={"obs": obs.astype("float32")},
          fetch_list=[self.value],
      )[0]
      pred_Q = np.squeeze(pred_Q, axis=0)
      act = np.argmax(pred_Q)  # 选择Q最大的下标，即对应的动作
      return act
  
file_path: PARL/examples/tutorials/homework/lesson3/dqn_mountaincar/agent.py
imports: import numpy
  import paddle.fluid
  import parl
  from parl import layers
label_desc: Use image node_id 4 for calling the Agent obj's underlying member method code with example usage: obj.predict(obs) and returns: act