code: def report(self):
      count = len(self.timings)
      if count == 0:
          return "No stats available"
  
      durations = [t["d"] for t in self.timings]
      average = sum(durations) / count
      fmt_str = (
          "Snapshot duration stats (sec): avg={:f}, min={:f}, max={:f}"
      )
      return fmt_str.format(average, min(durations), max(durations))
  
imports: import errno
  import os
  import shutil
  import tempfile
  import time
  import warnings
  import chainer
  from chainer.training import extension
label_desc: Use image node_id 4 for calling the _CheckpointStats obj's underlying member method code with example usage: obj.report() and returns: fmt_str, str