code: def create_trainer(self):
      try:
          p = self.output.parameters
          # Three of four parameters are learned by block_momentum_distributed_learner.
          bmd_learner = cntk.block_momentum_distributed_learner(
              cntk.momentum_sgd(
                  [p[0], p[1], p[2]],
                  cntk.learning_parameter_schedule(0.0001),
                  cntk.momentum_as_time_constant_schedule(1000),
              ),
              block_size=1000,
              block_learning_rate=0.01,
              block_momentum_as_time_constant=1000,
          )
  
          # New API to mark which learner is to use for metric aggregaion.
          bmd_learner.set_as_metric_aggregator()
  
          # The last parameter is learned by the data_parallel_distributed_learner.
          momentum_schedule = cntk.momentum_schedule_per_sample(
              0.9990913221888589
          )
          lr_per_sample = cntk.learning_parameter_schedule_per_sample(
              0.007
          )
          dpd_learner = cntk.data_parallel_distributed_learner(
              cntk.momentum_sgd(
                  [p[3]], lr_per_sample, momentum_schedule, True
              )
          )
  
          comm_rank = cntk.distributed.Communicator.rank()
          self.trainer = cntk.Trainer(
              self.output,
              (self.ce, self.err),
              [bmd_learner, dpd_learner],
              [
                  cntk.logging.ProgressPrinter(
                      freq=progress_freq, tag="Training", rank=comm_rank
                  )
              ],
          )
      except RuntimeError:
          self.trainer = None
      return
  
imports: import pytest
  import cntk
  import numpy
  import sys, os
  import argparse
  import re
  import platform
  from distributed_learner_test import mpiexec_execute
  from bmuf_metrics_aggregation_test import get_minibatch
label_desc: Use image node_id 2 for calling the MultiLearnerTrainer obj's underlying member method code with example usage: obj.create_trainer() without return types