code: def end(self):
      e = time.time()
  
      if self.begin is None:
          return
  
      self.timings.append({"b": self.begin, "d": e - self.begin})
      self.begin = None
  
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 3 for calling the _CheckpointStats obj's underlying member method code with example usage: obj.end() without return types