From b5dd5faba9b55fbffa28e943d1fb9e7723dc41e1 Mon Sep 17 00:00:00 2001
From: santhreal <64453045+santhreal@users.noreply.github.com>
Date: Fri, 17 Jul 2026 18:56:53 -0700
Subject: [PATCH] Fix TypeError when a keypath sets a string subkey through a
 list value

Setting a keypath whose parent value is a list but whose next key is a
non-integer string (e.g. b['a.x'] = 1 with a=[1, 2]) raised a raw
TypeError: list indices must be integers or slices, not str, while the
same assignment over a scalar/None value overrides it with a new dict.
A list cannot hold a string key, so treat it like a scalar and override
it, keeping the behavior consistent (b['a.x'] -> {'a': {'x': 1}}). Valid
integer indexes still address the list unchanged.
---
 benedict/dicts/keylist/keylist_util.py   |  6 +++++-
 tests/dicts/keypath/test_keypath_dict.py | 17 +++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/benedict/dicts/keylist/keylist_util.py b/benedict/dicts/keylist/keylist_util.py
index cfa773c1..9d8b9aa1 100644
--- a/benedict/dicts/keylist/keylist_util.py
+++ b/benedict/dicts/keylist/keylist_util.py
@@ -28,7 +28,11 @@ def _get_item_key_and_value(item: Any, key: Any) -> tuple[Any, Any]:
 def _get_or_new_item_value(item: Any, key: Any, subkey: Any) -> Any:
     try:
         _, value = _get_item_key_and_value(item, key)
-        if not type_util.is_dict_or_list_or_tuple(value):
+        # a list can only hold an integer-index subkey; anything else needs a dict
+        keeps_subkey = type_util.is_dict(value) or (
+            type_util.is_list_or_tuple(value) and _get_index(subkey) is not None
+        )
+        if not keeps_subkey:
             raise TypeError
     except (IndexError, KeyError, TypeError):
         value = _new_item_value(subkey)
diff --git a/tests/dicts/keypath/test_keypath_dict.py b/tests/dicts/keypath/test_keypath_dict.py
index 639cd1eb..9c6a703e 100644
--- a/tests/dicts/keypath/test_keypath_dict.py
+++ b/tests/dicts/keypath/test_keypath_dict.py
@@ -499,6 +499,23 @@ def test_setitem_override_existing_item(self) -> None:
         r = {"a": {"b": {"c": {"d": 3}}}}
         self.assertEqual(b, r)
 
+    def test_setitem_string_subkey_overrides_list_value(self) -> None:
+        # a string subkey cannot index a list, so it overrides the list like a scalar
+        b = KeypathDict({"a": [1, 2]})
+        b["a.x"] = 1
+        self.assertEqual(b, {"a": {"x": 1}})
+        b = KeypathDict({"a": [1, 2]})
+        b["a.x.y"] = 1
+        self.assertEqual(b, {"a": {"x": {"y": 1}}})
+        # a list-of-scalar element is likewise overridden by a string subkey
+        b = KeypathDict({"a": [5]})
+        b["a[0].x"] = 3
+        self.assertEqual(b, {"a": [{"x": 3}]})
+        # a valid integer index keeps the list
+        b = KeypathDict({"a": [1, 2]})
+        b["a[0]"] = 9
+        self.assertEqual(b, {"a": [9, 2]})
+
     def test_setitem_with_keys_list(self) -> None:
         d: dict[str, Any] = {
             "a": {