message: fix map_func in `read_batch_features`.
diff: @@ -688,6 +688,11 @@ class Dataset(object):
  else:
  dataset = reader(filenames)
  dataset = dataset.repeat(num_epochs)
  + if dataset.output_types == (dtypes.string, dtypes.string):
  + dataset = dataset.map(lambda unused_k, v: v)
  + elif dataset.output_types != dtypes.string:
  + raise TypeError("`reader` must be a dataset of `tf.string` values, "
  + "or `(tf.string, tf.string)` key-value pairs.")
  if randomize_input:
  dataset = dataset.shuffle(capacity)
  dataset = dataset.map(lambda x: _parse_example(nest.flatten(x), features))
  