code: def multi_node_mean_grad(self, model, zero_fill=False):
      stream = chainer.cuda.Stream.null
      self._multi_node_mean_grad_async(model, zero_fill, stream)
  
file_path: chainer/chainermn/communicators/pure_nccl_communicator.py
imports: import warnings
  import chainer.cuda
  from chainermn.communicators import _communication_utility
  from chainermn.communicators import _memory_utility
  from chainermn.communicators import mpi_communicator_base
  from chainermn import nccl
  import numpy
label_desc: Use image node_id 7 for calling the PureNcclCommunicator obj's underlying member method code with example usage: obj.multi_node_mean_grad(model, zero_fill) without return types