[Harshil Kaneria (Harshil26202)]

Motivation and Context

#14571 reported that filters with a negative number literal, such as lambda x: x.price > -5, raised NotImplementedError in most vector store connectors. #14572 fixed it by folding UnaryOp(USub, Constant(n)) into Constant(-n) in VectorSearch._build_filter.

InMemoryCollection doesn't go through _build_filter. It parses string filters in _parse_and_validate_filter and checks every node against allowed_filter_ast_nodes, which doesn't include USub. So the same filter still fails there when it is passed as a string, which is also the form the generated search functions pass:

await collection.search(vector=[1, 1], filter="lambda x: x.temp > -5")
# VectorStoreOperationException: Error evaluating filter: AST node type 'USub' is not allowed in filter expressions.

await collection.search(vector=[1, 1], filter=lambda x: x.temp > -5)  # works

Description

_parse_and_validate_filter now runs the existing _FoldUnaryNumericConstants transform on the parsed tree before the allowlist check. Only a unary minus applied directly to an int or float literal is folded, so the sandbox is unchanged: USub stays off the allowlist, and something like lambda x: -x.price > 1 is still rejected.

Tests in tests/unit/connectors/memory/test_in_memory.py:

• test_string_filter_with_negative_literal covers an int bound, a float equality and a chained comparison. All three fail on main and pass with this change.
• test_string_filter_still_rejects_unary_minus_on_a_field checks that unary minus on a field is still blocked.

Locally, tests/unit/data plus the in-memory, Qdrant, Qdrant local, Chroma and FAISS connector tests pass (253 passed). ruff check, ruff format --check and mypy are clean on the changed files.

AI disclosure: I found this with Claude Code while comparing filter results across the Python vector store connectors. It also drafted the fix and the tests.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[Copilot]

🟢 Approval recommended

No active review issues are reported for the change adding negative numeric literal support to InMemoryCollection filters.

No open issues 🎉

What changed in this PR

This PR extends the negative-literal filter fix from #14572 to InMemoryCollection, which validates string filters through a separate parsing path.

Changes:

• Reuses _FoldUnaryNumericConstants before AST allowlist validation to support negative numeric literals.
• Adds tests for integer bounds, float equality, and chained comparisons, plus a regression test confirming unary minus on fields remains rejected.

File	Description
python/​tests/​unit/​connectors/​memory/​test_in_memory.py	Tests negative-literal filters and continued rejection of field negation.
python/​semantic_kernel/​connectors/​in_memory.py	Folds negative numeric literals before validating string filters.

_{Review effort: Balanced}

[Mangesh Raut (mangeshraut712)]

The InMemory path needed this fold, and the tests correctly keep unary minus on a field rejected. One gap in the shared helper: it only folds USub, not UAdd.

[Mangesh Raut (mangeshraut712)]

_FoldUnaryNumericConstants (in semantic_kernel.data.vector) only folds UnaryOp(USub, Constant(n)). Python also parses +1 as UnaryOp(UAdd, Constant(1)), and the helper's own docstring talks about parsers that reject unary +/- wholesale. So lambda x: x.vector[0] > +1 still fails the allowlist after this visit, while -1 now works. Other connectors that already call this helper have the same gap. I'd fold UAdd of an int/float constant to Constant(+n) as well, and add a +1 / +2.5 case next to the negative-literal tests (plus a check that -x.vector[0] still raises).

[Harshil Kaneria (Harshil26202)]

Thanks for looking. You're right that +1 still fails here, but that matches every other connector today. The shared helper deliberately leaves unary plus alone: test_fold_unary_numeric_constants_preserves_other_unary_expressions in tests/unit/data/test_vector_negative_filter_literals.py (added with #14572) asserts that +5 and +5.5 are not folded.

This PR only brings InMemoryCollection in line with the other connectors, so I'd rather not change that shared behaviour here. If the maintainers want +n folded too, it's a small follow-up to the helper and that test, and I'm happy to open it.

[Harshil Kaneria (Harshil26202)]

@microsoft-github-policy-service agree