message: Implement shapes, classes, and types for output
diff: @@ -31,12 +31,14 @@ class LMDBDataset(dataset_ops.DatasetSource):
  def __init__(self, filenames):
  """Create a `LMDBDataset`.
  +
  `LMDBDataset` allows a user to read data from a mdb file as
  (key value) pairs sequentially.
  +
  For example:
  ```python
  tf.enable_eager_execution()
  - dataset = tf.contrib.lmdb.LMDBDataset("/foo/bar.mdb")
  + dataset = LMDBDataset("/foo/bar.mdb")
  # Prints the (key, value) pairs inside a lmdb file.
  for key, value in dataset:
  print(key, value)
  @@ -47,14 +49,18 @@ class LMDBDataset(dataset_ops.DatasetSource):
  super(LMDBDataset, self).__init__()
  self._filenames = ops.convert_to_tensor(
  filenames, dtype=dtypes.string, name="filenames")
  - variant_tensor = gen_experimental_dataset_ops.experimental_lmdb_dataset(
  - self._filenames, **dataset_ops.flat_structure(self))
  def _as_variant_tensor(self):
  return lmdb_ops.lmdb_dataset( self._filenames)
  @property
  - def _element_structure(self):
  - return structure.NestedStructure(
  - (structure.TensorStructure(dtypes.string, []),
  - structure.TensorStructure(dtypes.string, [])))
  + def output_classes(self):
  + return ops.Tensor, ops.Tensor
  +
  + @property
  + def output_shapes(self):
  + return (tensor_shape.TensorShape([]), tensor_shape.TensorShape([]))
  +
  + @property
  + def output_types(self):
  + return dtypes.string, dtypes.string
  