code: def stats(self):
          
          ret = '{name}:\n' \
              '  sample_num={sample_num}, batch_num={batch_num}\n' \
              '  key={bucket_keys}\n' \
              '  cnt={bucket_counts}\n' \
              '  batch_size={bucket_batch_sizes}'\
              .format(name=self.__class__.__name__,
                      sample_num=len(self._lengths),
                      batch_num=len(self._batch_infos),
                      bucket_keys=self._bucket_keys,
                      bucket_counts=[len(sample_ids) for sample_ids in self._bucket_sample_ids],
                      bucket_batch_sizes=self._bucket_batch_sizes)
          return ret
docs: Return a string representing the statistics of the bucketing sampler.
  
          Returns
          -------
          ret : str
              String representing the statistics of the buckets.