fix data_format parsing; remove auto_shard option

Author: Lee Yang

examples/mnist/keras/mnist_tf_ds.py

@@ -39,14 +39,14 @@ def parse_tfos(example_proto):
   # tfos: /path/to/mnist/tfr/train/part-r-*
   image_pattern = ctx.absolute_path(args.images_labels)
 
-  options = tf.data.Options()
-  options.experimental_distribute.auto_shard = False
-
   ds = tf.data.Dataset.list_files(image_pattern)
-  ds = ds.with_options(options)
   ds = ds.repeat(args.epochs).shuffle(BUFFER_SIZE)
   ds = ds.interleave(tf.data.TFRecordDataset)
-  train_datasets_unbatched = ds.map(parse_tfos)
+
+  if args.data_format == 'tfds':
+    train_datasets_unbatched = ds.map(parse_tfds)
+  else:  # 'tfos'
+    train_datasets_unbatched = ds.map(parse_tfos)
 
   def build_and_compile_cnn_model():
     model = tf.keras.Sequential([