From 0dd9dfdfc745f002afd24facc918744a8fe1ccfc Mon Sep 17 00:00:00 2001
From: "lancedb-gatefixer[bot]"
 <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>
Date: Thu, 27 Aug 2026 17:10:51 +0800
Subject: [PATCH] test(python): cover arithmetic with distance projections
 (#3862)
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## Summary

- add Python regression coverage for integer and double arithmetic
against the generated _distance column
- merge the current main base containing Lance v11.0.0-beta.3 from #3896
- verify both expressions retain the generated scoring field Float32
type and compute the expected values

## Root cause

Lance parsed dynamic projection expressions before vector search added
its generated Float32 _distance field. Without a typed provisional
field, expression discovery rejected mixed numeric arithmetic. Lance
upstream fixed discovery and final-schema replanning in
lance-format/lance#8163, and the current base consumes that fix through
Lance v11.0.0-beta.3.

## Validation

- uv run --extra tests pytest
python/tests/test_query.py::test_select_arithmetic_with_distance -vv
--maxfail=2 — 2 passed
- python/.venv/bin/ruff format --check python/python/tests/test_query.py
- python/.venv/bin/ruff check .

Fixes #2618

<!-- lance-gatekeeper-fix:v1 agent=816a060090517471edfb73652bb5c9fe
generation=1 -->

---------

Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>
Co-authored-by: Xuanwo <github@xuanwo.io>
---
 python/python/tests/test_query.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/python/python/tests/test_query.py b/python/python/tests/test_query.py
index 4758f0e2d..ff62b2b51 100644
--- a/python/python/tests/test_query.py
+++ b/python/python/tests/test_query.py
@@ -675,6 +675,21 @@ def test_distance_range(table: lancedb.table.Table):
     assert res["_distance"].to_pylist() == [min_dist, max_dist]
 
 
+@pytest.mark.parametrize("expression", ["1 - _distance", "1.0 - _distance"])
+def test_select_arithmetic_with_distance(table, expression):
+    result = (
+        table.search([10, 10])
+        .select({"similarity": expression, "_distance": "_distance"})
+        .distance_type("cosine")
+        .to_arrow()
+    )
+
+    assert result.schema.field("similarity").type == pa.float32()
+    assert result["similarity"].to_pylist() == pytest.approx(
+        [1 - distance for distance in result["_distance"].to_pylist()]
+    )
+
+
 @pytest.mark.asyncio
 async def test_distance_range_async(table_async: AsyncTable):
     q = [0, 0]