code: def _buildRing(self, num_workers, num_gpus, subdiv):
      gpu_perm = range(0, num_gpus)
      return lambda x, un_op: ar.build_ring_all_reduce(
          x, num_workers, subdiv, gpu_perm, math_ops.add, un_op
      )
  
imports: import time
  import numpy
  from tensorflow.core.framework import types_pb2
  from tensorflow.python.distribute.v1 import all_reduce
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import state_ops
  from tensorflow.python.platform import test
  from tensorflow.python.platform import tf_logging
label_desc: Use image node_id 6 for calling the AllReduceTest obj's underlying member method code with example usage: obj._buildRing(num_workers, num_gpus, subdiv) and returns: function