class ReadInstruction:
    """Reading instruction for a dataset.

    Examples::

      # The following lines are equivalent:
      ds = datasets.load_dataset('mnist', split='test[:33%]')
      ds = datasets.load_dataset('mnist', split=datasets.ReadInstruction.from_spec('test[:33%]'))
      ds = datasets.load_dataset('mnist', split=datasets.ReadInstruction('test', to=33, unit='%'))
      ds = datasets.load_dataset('mnist', split=datasets.ReadInstruction(
          'test', from_=0, to=33, unit='%'))

      # The following lines are equivalent:
      ds = datasets.load_dataset('mnist', split='test[:33%]+train[1:-1]')
      ds = datasets.load_dataset('mnist', split=datasets.ReadInstruction.from_spec(
          'test[:33%]+train[1:-1]'))
      ds = datasets.load_dataset('mnist', split=(
          datasets.ReadInstruction('test', to=33, unit='%') +
          datasets.ReadInstruction('train', from_=1, to=-1, unit='abs')))