From f485693fa0c810279a2e74d2d88385ab89fd56e7 Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Wed, 4 Apr 2018 06:46:50 -0500
Subject: [PATCH] Support void materials in C API Python bindings

---
 openmc/capi/cell.py     | 13 +++++++------
 openmc/capi/material.py |  3 +++
 src/geometry_header.F90 | 14 +++++---------
 3 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/openmc/capi/cell.py b/openmc/capi/cell.py
index 8f0c0e1bb4..ccc6b6f6eb 100644
--- a/openmc/capi/cell.py
+++ b/openmc/capi/cell.py
@@ -115,14 +115,15 @@ class Cell(_FortranObjectWithID):
     def fill(self, fill):
         if isinstance(fill, Iterable):
             n = len(fill)
-            indices = (c_int*n)(*(m._index for m in fill))
-            _dll.openmc_cell_set_fill(self._index, 1, 1, indices)
+            indices = (c_int32*n)(*(m._index if m is not None else -1
+                                    for m in fill))
+            _dll.openmc_cell_set_fill(self._index, 1, n, indices)
         elif isinstance(fill, Material):
-            materials = [fill]
-            indices = (c_int*1)(fill._index)
+            indices = (c_int32*1)(fill._index)
+            _dll.openmc_cell_set_fill(self._index, 1, 1, indices)
+        elif fill is None:
+            indices = (c_int32*1)(-1)
             _dll.openmc_cell_set_fill(self._index, 1, 1, indices)
-        else:
-            raise NotImplementedError
 
     def set_temperature(self, T, instance=None):
         """Set the temperature of a cell
diff --git a/openmc/capi/material.py b/openmc/capi/material.py
index 62d6df012a..464b8a1a33 100644
--- a/openmc/capi/material.py
+++ b/openmc/capi/material.py
@@ -89,6 +89,9 @@ class Material(_FortranObjectWithID):
                 index = index.value
             else:
                 index = mapping[uid]._index
+        elif index == -1:
+            # Special value indicates void material
+            return None
 
         if index not in cls.__instances:
             instance = super(Material, cls).__new__(cls)
diff --git a/src/geometry_header.F90 b/src/geometry_header.F90
index e71916d096..f6206adf99 100644
--- a/src/geometry_header.F90
+++ b/src/geometry_header.F90
@@ -544,16 +544,12 @@ contains
           c % type = FILL_MATERIAL
           do i = 1, n
             j = indices(i)
-            if (j == 0) then
-              c % material(i) = MATERIAL_VOID
+            if ((j >= 1 .and. j <= n_materials) .or. j == MATERIAL_VOID) then
+              c % material(i) = j
             else
-              if (j >= 1 .and. j <= n_materials) then
-                c % material(i) = j
-              else
-                err = E_OUT_OF_BOUNDS
-                call set_errmsg("Index " // trim(to_str(j)) // " in the &
-                     &materials array is out of bounds.")
-              end if
+              err = E_OUT_OF_BOUNDS
+              call set_errmsg("Index " // trim(to_str(j)) // " in the &
+                   &materials array is out of bounds.")
             end if
           end do
         case (FILL_UNIVERSE)