Address review comments

Author: Balaji Veeramani

src/sagemaker/serializers.py

@@ -64,33 +64,32 @@ def serialize(self, data):
                 file, or buffer.
 
         Returns:
-            _io.BytesIO: A buffer containing data serialzied in the .npy format.
+            io.BytesIO: A buffer containing data serialzied in the .npy format.
         """
         if isinstance(data, np.ndarray):
             if not data.size > 0:
                 raise ValueError("Cannot serialize empty array.")
-            return self.serialize_array(data)
+            return self._serialize_array(data)
 
         if isinstance(data, list):
             if not len(data) > 0:
-                raise ValueError("empty array can't be serialized")
-            return self.serialize_array(np.array(data, self.dtype))
+                raise ValueError("Cannot serialize empty array.")
+            return self._serialize_array(np.array(data, self.dtype))
 
         # files and buffers. Assumed to hold npy-formatted data.
         if hasattr(data, "read"):
             return data.read()
 
-        return self.serialize_array(np.array(data))
+        return self._serialize_array(np.array(data))
 
-    @staticmethod
-    def serialize_array(array):
+    def _serialize_array(self, array):
         """Saves a NumPy array in a buffer.
 
         Args:
             array (numpy.ndarray): The array to serialize.
 
         Returns:
-            _io.BytesIO: A buffer containing the serialized array.
+            io.BytesIO: A buffer containing the serialized array.
         """
         buffer = io.BytesIO()
         np.save(buffer, array)