code: def prepare_backward(
      self, backward_sequence, parameter_zero_grad=True
  ):
      for v in backward_sequence.unused_variables:
          v.need_grad = False
      for p in backward_sequence.parameters:
          p.need_grad = True
          if parameter_zero_grad:
              p.grad.zero()
      for v in backward_sequence.variables:
          v.need_grad = True
  
      # We think this should be a bug
      # for l in backward_sequence.loss_variables:
      #     l.grad.fill(1.0 / l.size)
      for l in backward_sequence.loss_variables:
          l.grad.fill(1.0)
  
file_path: nnabla/python/test/core/legacy_network.py
imports: from nnabla.logger import logger
  import nnabla.function
label_desc: Use image node_id 8 for calling the Network obj's underlying member method code with example usage: obj.prepare_backward(backward_sequence, parameter_zero_grad) without return types