class_docstr: Dataset of a dictionary of datasets.
  
  It combines multiple datasets into one dataset. Each example is represented
  by a dictionary mapping a key to an example of the corresponding dataset.
  
  Args:
      datasets: Underlying datasets. The keys are used as the keys of each
          example. All datasets must have the same length.
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code: def __init__(self, **datasets):
      if not datasets:
          raise ValueError("no datasets are given")
      length = None
      for key, dataset in six.iteritems(datasets):
          if length is None:
              length = len(dataset)
          elif length != len(dataset):
              raise ValueError(
                  'dataset length conflicts at "{}"'.format(key)
              )
      self._datasets = datasets
      self._length = length
  
imports: import six
label_desc: Use image node_id 1 to create a new DictDataset object from inherited base classes: object with example: obj = DictDataset()