docstr: 使用policy model预测输出的动作概率
          
docstr_tok: ["\u4f7f\u7528policy","model\u9884\u6d4b\u8f93\u51fa\u7684\u52a8\u4f5c\u6982\u7387"]
code: def predict(self, obs):
      """使用policy model预测输出的动作概率"""
      return self.model(obs)
  
file_path: PARL/examples/tutorials/lesson4/policy_gradient/algorithm.py
imports: import paddle.fluid
  import parl
  from parl import layers
label_desc: Use image node_id 2 for calling the PolicyGradient obj's underlying member method code with example usage: obj.predict(obs) and returns: self