From 962d592d2e262206dcde01207100e14cf26a91b0 Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Tue, 10 May 2016 11:21:48 -0500
Subject: [PATCH] Restrict the Cell.rotation property to cells filled with a
 Universe

---
 openmc/cell.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/openmc/cell.py b/openmc/cell.py
index 806f3f32ff..8ddae63716 100644
--- a/openmc/cell.py
+++ b/openmc/cell.py
@@ -243,6 +243,10 @@ class Cell(object):
 
     @rotation.setter
     def rotation(self, rotation):
+        if not isinstance(self.fill, openmc.Universe):
+            raise RuntimeError('Cell rotation can only be applied if the cell '
+                               'is filled with a Universe')
+
         cv.check_type('cell rotation', rotation, Iterable, Real)
         cv.check_length('cell rotation', rotation, 3)
         self._rotation = rotation