code: def _save_model(args, rank=0):
      if args.model_prefix is None:
          return None
      return mx.callback.do_checkpoint(
          args.model_prefix
          if rank == 0
          else "%s-%d" % (args.model_prefix, rank),
          period=args.save_period,
      )
  
file_path: byteps/example/mxnet/common/fit.py
imports: import logging
  import os
  import time
  import re
  import math
  import mxnet
label_desc: Use image node_id 4 for calling a global function with example usage: _save_model(args, rank) and returns: mx, None