Update metrics.py

Add assert message.
diff --git a/tensorflow/python/keras/metrics.py b/tensorflow/python/keras/metrics.py
index 1fbd515..d267ab6 100644
--- a/tensorflow/python/keras/metrics.py
+++ b/tensorflow/python/keras/metrics.py
@@ -3342,7 +3342,8 @@
   Returns:
     Categorical accuracy values.
   """
-  assert y_true.shape==y_pred.shape
+  #assert if both have same shape
+  assert y_true.shape==y_pred.shape,"Both inputs must have same shapes and must be one-hot encoded. Use tf.one_hot() to one hot encode the inputs."
   
   return math_ops.cast(
       math_ops.equal(