docstr: get loss variable
docstr_tok: ["get","loss","variable"]
code: def loss(self):
      "get loss variable"
      raise NotImplementedError(self, self.loss)
  
imports: import os
  import logging
  import paddle.fluid
label_desc: Use image node_id 6 for calling the ModelBase obj's underlying member method code with example usage: obj.loss() without return types