message: [tf.contrib.data] map expects a nested structure.
  Fixes
diff: @@ -548,8 +548,8 @@ labels = [0, 37, 29, 1, ...]
  dataset = tf.contrib.data.Dataset.from_tensor_slices((filenames, labels))
  dataset = dataset.map(
  - lambda filename, label: tf.py_func(
  - _read_py_function, [filename, label], [tf.uint8, label.dtype]))
  + lambda filename, label: tuple(tf.py_func(
  + _read_py_function, [filename, label], [tf.uint8, label.dtype])))
  dataset = dataset.map(_resize_function)
  ```
  