Add type checking at the beginning of tpu.shard().

Otherwise a message like "TypeError: Tensor objects are only iterable when eager execution is enabled. To iterate over this tensor use tf.map_fn." will be thrown, which is confusing.

PiperOrigin-RevId: 213371676

1 files changed, 5 insertions, 1 deletions

diff --git a/tensorflow/contrib/tpu/python/tpu/tpu.py b/tensorflow/contrib/tpu/python/tpu/tpu.py
index 815a087a24..593f1d909e 100644
--- a/tensorflow/contrib/tpu/python/tpu/tpu.py
+++ b/tensorflow/contrib/tpu/python/tpu/tpu.py
@@ -847,8 +847,12 @@ def shard(computation,
   if num_shards <= 0:
     raise ValueError("num_shards must be a positive integer.")
 
+  inputs = [] if inputs is None else inputs
+  if not isinstance(inputs, list):
+    raise TypeError("tpu.shard()'s inputs must be a list of Tensors or None.")
+
   # Converts inputs to Tensors.
-  inputs = [] if inputs is None else [ops.convert_to_tensor(x) for x in inputs]
+  inputs = [ops.convert_to_tensor(x) for x in inputs]
 
   if input_shard_axes is None:
     input_shard_axes = [0] * len(inputs)