code: def __len__(self):
      return 10
  
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 1 for calling the SampleDataset obj's underlying member method code with example usage: obj.__len__() and returns: int