diff --git a/python/resdata/grid/rd_region.py b/python/resdata/grid/rd_region.py
index 69ad6e24b..18aca7f69 100644
--- a/python/resdata/grid/rd_region.py
+++ b/python/resdata/grid/rd_region.py
@@ -1173,9 +1173,7 @@ def contains_active(self, active_index):
         return self._contains_active(active_index)
 
     def kw_index_list(self, rd_kw, force_active):
-        c_ptr = self._get_kw_index_list(rd_kw, force_active)
-        index_list = IntVector.createCReference(c_ptr, self)
-        return index_list
+        return self._get_kw_index_list(rd_kw, force_active)
 
     @property
     def name(self):
diff --git a/python/tests/rd_tests/test_rd_kw.py b/python/tests/rd_tests/test_rd_kw.py
index 7adb45cef..e857f262f 100644
--- a/python/tests/rd_tests/test_rd_kw.py
+++ b/python/tests/rd_tests/test_rd_kw.py
@@ -8,6 +8,7 @@
 import random
 
 from resdata import ResDataType, ResdataTypeEnum, FileMode
+from resdata.grid import ResdataRegion, GridGenerator
 from resdata.resfile import ResdataKW, ResdataFile, FortIO, openFortIO
 
 
@@ -645,6 +646,39 @@ def test_imul():
         kw2 *= "a"
 
 
+def test_assign():
+    kw1 = ResdataKW("KW1", 5, ResDataType.RD_INT)
+    kw2 = ResdataKW("KW2", 6, ResDataType.RD_INT)
+    kw3 = ResdataKW("KW3", 5, ResDataType.RD_FLOAT)
+    for i in range(len(kw1)):
+        kw1[i] = 1
+    with pytest.raises(TypeError, match="Type / size mismatch"):
+        kw2.assign(kw1)
+    with pytest.raises(TypeError, match="Type / size mismatch"):
+        kw3.assign(kw1)
+    with pytest.raises(TypeError, match="Type mismatch"):
+        kw2.assign("a")
+    with pytest.raises(TypeError, match="Only muliplication with scalar supported"):
+        kw3.assign("a")
+
+
+def test_apply():
+    kw1 = ResdataKW("KW1", 5, ResDataType.RD_INT)
+    kw2 = ResdataKW("KW2", 6, ResDataType.RD_INT)
+    kw3 = ResdataKW("KW3", 5, ResDataType.RD_FLOAT)
+    kw1.assign(1)
+    kw1.apply(lambda x: x + 1)
+    assert list(kw1) == [2] * 5
+    kw2.assign(5)
+    kw2.apply(lambda x, y: x + y, arg=5)
+    assert list(kw2) == [10] * 6
+    grid = GridGenerator.create_rectangular(dims=(5, 1, 1), dV=(1, 1, 1))
+    region = ResdataRegion(grid, True)
+    kw3.assign(3.0)
+    kw3.apply(lambda x: x + 1.0, mask=region)
+    assert list(kw3) == [4.0] * 5
+
+
 def test_get_ptr_data():
     assert ResdataKW("KW1", 10, ResDataType.RD_INT).get_data_ptr()
     assert ResdataKW("KW1", 10, ResDataType.RD_FLOAT).get_data_ptr()
diff --git a/python/tests/rd_tests/test_region.py b/python/tests/rd_tests/test_region.py
index 840c70e74..46d0a1ec5 100644
--- a/python/tests/rd_tests/test_region.py
+++ b/python/tests/rd_tests/test_region.py
@@ -517,3 +517,10 @@ def test_get_set_name(full_region):
 
 def test_contains_active(full_region):
     assert full_region.contains_active(0)
+
+
+def test_kw_index_list(grid, full_region):
+    kw_int = ResdataKW("INT", grid.get_global_size(), ResDataType.RD_INT)
+    kw_float = ResdataKW("FLOAT", grid.get_global_size(), ResDataType.RD_FLOAT)
+    full_region.kw_index_list(kw_int, False)
+    full_region.kw_index_list(kw_float, True)