code: def __len__(self):
      return self.data.shape[1]
  
file_path: chainer/tests/chainer_tests/dataset_tests/tabular_tests/dummy_dataset.py
imports: import numpy
  import chainer
  from chainer import testing
label_desc: Use image node_id 2 for calling the DummyDataset obj's underlying member method code with example usage: obj.__len__() and returns: self