fix: handle non-string dict keys holding lists in keylists/keypaths

[Sanjays2402]

Summary

keylists(d, indexes=True) raises TypeError whenever a non-string dict key (int / None / bool / tuple) holds a list value. Because keypaths, match, and the public benedict.keypaths() / benedict.keylists() all build on keylists, the crash also surfaces through the public API.

Reproduce

from benedict import benedict

benedict({0: [1, 2]}).keypaths(indexes=True)
# TypeError: unsupported operand type(s) for +=: 'int' and 'str'

from benedict.core.keylists import keylists
keylists({0: [1, 2]}, indexes=True)      # TypeError
keylists({None: [1, 2]}, indexes=True)   # TypeError

Root cause

In benedict/core/keylists.py, _get_keylist_for_list appended the list index to the parent key with:

keys[-1] += f"[{key}]"

This assumes the last parent key is a string. A string key "a" becomes "a[0]", but an int key 0 evaluates 0 += "[0]" and crashes.

The behaviour was inconsistent: the same non-string key holding a dict worked fine, and non-string keys are explicitly supported elsewhere in the module (see the existing test_keylists_with_non_string_keys). Only the list branch assumed stringness.

input	keylists(..., indexes=True) before	after
{"a": [1, 2]}	[['a'], ['a[0]'], ['a[1]']]	[['a'], ['a[0]'], ['a[1]']] (unchanged)
{0: {"x": 1}}	[[0], [0, 'x']]	[[0], [0, 'x']] (unchanged)
{0: [1, 2]}	TypeError	[[0], ['0[0]'], ['0[1]']]
{None: [1, 2]}	TypeError	[[None], ['None[0]'], ['None[1]']]

Fix

Stringify the parent key before appending the index:

keys[-1] = f"{keys[-1]}[{key}]"

String keys are unaffected (f"{'a'}[0]" == "a[0]"); non-string keys now produce a consistent stringified keypath (0 → "0[0]", None → "None[0]"), matching how keypaths already stringifies every key via f"{key}".

Tests

Added test_keylists_with_non_string_keys_and_lists_and_indexes_included, which follows the existing test_keylists_with_non_string_keys membership style (mixed int/str/None keylists can't be sorted for comparison).

Proven to guard the bug — stash the source fix and the new test fails with the original TypeError at keylists.py:26; restore the fix and it passes:

# without fix
FAILED tests/core/test_keylists.py::keylists_test_case::test_keylists_with_non_string_keys_and_lists_and_indexes_included
  E   TypeError: unsupported operand type(s) for +=: 'int' and 'str'
  benedict/core/keylists.py:26: TypeError

# with fix
tests/core/test_keylists.py ... 1 passed

Full tests/core + tests/utils suite: 123 passed (was 122). ruff check, ruff format --check, black --check and mypy are all clean on the changed files (the 3 pre-existing mypy errors in serializers/* and parse_util.py are unrelated optional-dependency stub issues, present with or without this change).

Diff: +27 / −1 across benedict/core/keylists.py and tests/core/test_keylists.py.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.32%. Comparing base (068813d) to head (3425c1f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #583   +/-   ##
=======================================
  Coverage   98.32%   98.32%           
=======================================
  Files          64       64           
  Lines        2392     2392           
=======================================
  Hits         2352     2352           
  Misses         40       40           

Flag	Coverage Δ
unittests	98.32% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

Fixes a TypeError in keylists(..., indexes=True) when traversing list values under non-string dict keys, which also affected the public benedict.keypaths() / benedict.keylists() APIs that build on keylists.

Changes:

• Update list-index key composition to stringify the parent key before appending "[i]", avoiding int += str (and similar) failures.
• Add a regression test covering non-string keys (e.g., 0, None) that hold list values when indexes=True.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
benedict/core/keylists.py	Prevents TypeError by building indexed list keys via an f-string assignment instead of += on potentially non-string keys.
tests/core/test_keylists.py	Adds regression coverage for non-string dict keys that hold lists when indexes=True.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.