code: def get_example_by_keys(self, i, key_indices):
      return tuple(
          "{:s}({:d})".format(self.keys[key_index], i)
          for key_index in key_indices
      )
  
imports: import numpy
  import six
  import unittest
  from chainercv.chainer_experimental.datasets.sliceable import SliceableDataset
  from chainercv.utils import testing
label_desc: Use image node_id 3 for calling the SampleDataset obj's underlying member method code with example usage: obj.get_example_by_keys(i, key_indices) and returns: tuple