docstr: Returns loss block to be used for specific head implementation.
  
  :return: loss block (can be called as function) for outputs returned by the head network.
docstr_tok: ["Returns","loss","block","to","be","used","for","specific","head","implementation",".",":","return",":","loss","block","(","can","be","called","as","function",")","for","outputs","returned","by","the","head","network","."]
code: def loss(self) -> HeadLoss:
      """
      Returns loss block to be used for specific head implementation.
  
      :return: loss block (can be called as function) for outputs returned by the head network.
      """
      raise NotImplementedError()
  
imports: from typing import Dict, List, Union, Tuple
  import mxnet
  from mxnet.initializer import Initializer, register
  from mxnet.gluon import nn, loss
  from mxnet.ndarray import NDArray
  from mxnet.symbol import Symbol
  from rl_coach.base_parameters import AgentParameters
  from rl_coach.spaces import SpacesDefinition
label_desc: Use image node_id 2 for calling the Head obj's underlying member method code with example usage: obj.loss() without return types