Enforce freezing before standalone keylist assignments

benedict/dicts/keylist/keylist_dict.py

@@ -61,6 +61,7 @@ def _getitem_bystreys(self, keys: Any) -> Any:
     def __setitem__(
         self, key: list[str | int] | tuple[str | int, ...] | _K, value: _V
     ) -> None:
+        self._check_frozen()
         if type_util.is_list(key):
             self._setitem_bystreys(key, value)
             return

tests/dicts/keylist/test_frozen_assignment.py

@@ -0,0 +1,29 @@
+import unittest
+
+from benedict.dicts import KeylistDict, KeypathDict
+
+
+class frozen_assignment_test_case(unittest.TestCase):
+    def test_frozen_nested_assignment(self) -> None:
+        for cls, key in [
+            (KeylistDict, ["nested", "value"]),
+            (KeypathDict, "nested.value"),
+        ]:
+            for data in [{"nested": {"value": 1}}, {"nested": {}}, {}]:
+                with self.subTest(cls=cls, data=data):
+                    obj = cls(data).freeze()
+                    before = repr(obj)
+                    with self.assertRaises(TypeError):
+                        obj[key] = 2
+                    self.assertEqual(repr(obj), before)
+
+    def test_frozen_list_assignment(self) -> None:
+        obj = KeylistDict({"items": [1]}).freeze()
+        with self.assertRaises(TypeError):
+            obj[["items", 0]] = 2
+        self.assertEqual(obj["items"], [1])
+
+    def test_assignment_after_unfreeze(self) -> None:
+        obj = KeypathDict({"nested": {"value": 1}}).freeze().unfreeze()
+        obj["nested.value"] = 2
+        self.assertEqual(obj["nested.value"], 2)