code: def learn(self, obs, label):
      pred_output = self.model.policy(obs)
      cost = layers.square_error_cost(obs, label)
      cost = fluid.layers.reduce_mean(cost)
      return cost
  
imports: import numpy
  import unittest
  from paddle import fluid
  from parl import layers
  import parl
  import os
label_desc: Use image node_id 3 for calling the TestAlgorithm obj's underlying member method code with example usage: obj.learn(obs, label) and returns: cost