[Python] Add support for negative indexing in ObjectTable

src/bindings/bnd_extensions.cpp

@@ -14,7 +14,7 @@ static bool SeekPastCompressedBuffer(ON_BinaryArchive& archive)
   size_t sizeof__outbuffer;
   if (!archive.ReadCompressedBufferSize(&sizeof__outbuffer))
     return false;
-  
+
   if (0 == sizeof__outbuffer)
     return true;
 
@@ -464,13 +464,13 @@ BND_UUID BND_ONXModel_ObjectTable::AddPolyline2(const std::vector<ON_3dPoint>& p
 BND_UUID BND_ONXModel_ObjectTable::AddPolyline3(emscripten::val points, const class BND_3dmObjectAttributes* attributes)
 {
   bool isArray = points.hasOwnProperty("length");
-  if( isArray ) 
+  if( isArray )
   {
     const std::vector<ON_3dPoint> array = emscripten::vecFromJSArray<ON_3dPoint>(points);
-    return AddPolyline2( array, attributes ); 
+    return AddPolyline2( array, attributes );
   }
   else
-    return AddPolyline1( points.as<const BND_Point3dList&>(), attributes ); 
+    return AddPolyline1( points.as<const BND_Point3dList&>(), attributes );
 }
 
 #endif
@@ -669,10 +669,7 @@ static BND_FileObject* FileObjectFromCompRef(ON_ModelComponentReference& compref
 
 BND_FileObject* BND_ONXModel_ObjectTable::ModelObjectAt(int index)
 {
-#if defined(ON_PYTHON_COMPILE)
-  if (index < 0)
-    throw py::index_error();
-#else
+#if !defined(ON_PYTHON_COMPILE)
   if (index < 0)
     return nullptr;
 #endif
@@ -700,6 +697,11 @@ BND_FileObject* BND_ONXModel_ObjectTable::ModelObjectAt(int index)
     }
   }
 
+#if defined(ON_PYTHON_COMPILE)
+  if (index < 0)
+    index = m_compref_cache.Count() + index < 0 ? std::abs(index) : m_compref_cache.Count() + index;
+#endif
+
   if (index < m_compref_cache.Count())
   {
     return FileObjectFromCompRef(m_compref_cache[index]);
@@ -1217,7 +1219,7 @@ int BND_File3dmInstanceDefinitionTable::Add(std::wstring name, std::wstring desc
   const int count_a = attributes["length"].as<int>();
 #endif
 
-  if(m_model && count_g > 0) 
+  if(m_model && count_g > 0)
   {
     // Determine if we need to transform geometry to world origin
     ON_Xform xf;
@@ -1230,17 +1232,17 @@ int BND_File3dmInstanceDefinitionTable::Add(std::wstring name, std::wstring desc
 
     ON_SimpleArray<ON_UUID> object_uuids;
 
-    for ( int i = 0; i < count_g; i ++ ) 
+    for ( int i = 0; i < count_g; i ++ )
     {
 
 #if defined(ON_PYTHON_COMPILE)
       BND_GeometryBase g = py::cast<BND_GeometryBase>(geometry[i]);
       BND_3dmObjectAttributes oa = py::cast<BND_3dmObjectAttributes>(attributes[i]);
 #else
-      BND_GeometryBase g = geometry[i].as<BND_GeometryBase>();  
+      BND_GeometryBase g = geometry[i].as<BND_GeometryBase>();
       BND_3dmObjectAttributes oa = attributes[i].as<BND_3dmObjectAttributes>();
 #endif
-      
+
       const ON_Geometry* pConstGeom = g.GeometryPointer();
       const ON_3dmObjectAttributes* pConstAtts = i < count_a ? oa.m_attributes : &ON_3dmObjectAttributes::DefaultAttributes;
 
@@ -1302,7 +1304,7 @@ int BND_File3dmInstanceDefinitionTable::Add(std::wstring name, std::wstring desc
       }
     }
   }
-  
+
   return index;
 }
 
@@ -1614,7 +1616,7 @@ BND_TUPLE BND_FileObject::GetTextureMapping( const class BND_File3dm* file3dm, i
 
   if(tm == ON_TextureMapping::Unset)
     return NullTuple();
-  else 
+  else
   {
     SetTuple(rc, 0, BND_TextureMapping(tm, nullptr));
     SetTuple(rc, 1, BND_Transform(m_object_xform));

tests/python/test_File3dm_ObjectTable.py

@@ -24,7 +24,28 @@ def test_addPolyline(self):
 
         self.assertTrue(objqty == 2 and isCurve1 and isCurve2 and len1 == 15 and len2 == 15)
 
+
+    def test_negativeIndexing(self) -> None:
+        """Tests for indexing `ObjectTable`.
+        """
+        file_3dm = rhino3dm.File3dm()
+        for i in range(2):
+            file_3dm.Objects.AddPoint(rhino3dm.Point3d(i, i, i))
+
+        with self.assertRaises(IndexError, msg="Test negative IndexError"):
+            file_3dm.Objects[-3]
+
+        with self.assertRaises(IndexError, msg="Test positive IndexError"):
+            file_3dm.Objects[3]
+
+        with self.subTest(msg="Test positive indexing"):
+            self.assertEqual(file_3dm.Objects[1].Geometry.Location, rhino3dm.Point3d(1, 1, 1))
+
+        with self.subTest(msg="Test negative indexing"):
+            self.assertEqual(file_3dm.Objects[-2].Geometry.Location, rhino3dm.Point3d(0, 0, 0))
+
+
 if __name__ == '__main__':
     print("running tests")
     unittest.main()
-    print("tests complete")
+    print("tests complete")