Match nothing instead of raising KeyError for Index on a dict (fixes #93)

[gaoflow]

Summary

Fixes #93. Index.find (the concrete [n] syntax) raises an uncaught KeyError when it is applied to a dict:

import jsonpath_ng
jsonpath_ng.parse("$.*[0].b").find({"a": [{"b": 1}], "c": {"d": 2}})
# KeyError: 0

The wildcard * matches every value (including the dict {"d": 2}), then [0] is applied to each — and indexing the dict raises. Minimal repro: jsonpath_ng.parse("[0]").find({"foo": 1}).

This contradicts the class's own docstring — "If the datum is None or not long enough, it will not crash but will not match anything" — and is inconsistent with the sibling paths: Slice ([*]) and Fields (.foo) both handle a dict datum gracefully. Only Index crashes.

Cause

In Index._find_base, the guard

if datum.value and len(datum.value) > index:
    rv += [DatumInContext(datum.value[index], ...)]

assumes anything with a len() is integer-indexable. A dict satisfies len(datum.value) > index, but datum.value[index] is then a key lookup that raises KeyError.

Fix

Return early when the datum is a dict — integer indices apply to sequences, not mappings, so (per the docstring) match nothing rather than crashing. Sequence and string indexing are untouched.

rv = []
if isinstance(datum.value, dict):
    return rv
for index in self.indices:
    ...

The fix is scoped to the find contract; find_or_create on an empty dict still converts it to a list first (in the create block above), so that path is unaffected.

Verification

• Added two cases to the find_test_cases table: ("[0]", {"foo": 1}, [], []) and the issue Expression with wildcard then index selection errors with KeyError #93 repro ("$.*[0].b", {"a": [{"b": 1}], "c": {"d": 2}}, [1], ["((a.[0]).b)"]). They fail with KeyError before the fix and pass after (confirmed via git stash).
• List/tuple/string indexing behavior is preserved.
• Full suite: 355 passed (was 351).
• Added a ### Fixed entry to CHANGELOG.md under [Unreleased].

This pull request was prepared with the assistance of AI, under my direction and review.