fix(python): translate Polars decimal literals (#10187)

Polars decimal comparisons fail because `Scalar.Decimal` is
unrecognized. Preserve the serialized unscaled integer, precision, and
scale in a native Vortex decimal literal, without floating-point
conversion.

This is a direct expression translation; it performs no eager evaluation
and does not require literal arguments. Literal-specific PRs decode the
scalar representation itself.

Validation: 1 targeted regression case(s) passed with this PR’s
converter. With only `polars_.py` restored to the base revision and the
same tests retained, all 1 failed with Polars `ComputeError` wrapping
the unsupported-expression `ValueError` or `NotImplementedError`. The
tests compare complete dataframes from Polars alone and a Vortex-backed
Polars scan, and check explicit row expectations. No lint or broader
suite was run.

Signed-off-by: Daniel King <dan@spiraldb.com>

Author: danking

vortex-python/python/vortex/polars_.py

@@ -101,6 +101,9 @@ def _polars_to_vortex(expr: dict[str, Any]) -> ve.Expr:
             dtype = "Int64"
         elif "Time" in scalar:
             return ve.literal(_dtype.time("ns"), scalar["Time"])
+        elif "Decimal" in scalar:
+            value, precision, scale = scalar["Decimal"]
+            return ve.literal(_dtype.decimal(precision=precision, scale=scale), value)
         else:
             raise ValueError(f"Cannot convert to Vortex: unsupported Polars scalar value type {scalar}")
 

vortex-python/test/test_polars_.py

@@ -4,6 +4,7 @@
 import math
 import os
 from datetime import time
+from decimal import Decimal
 
 import polars as pl
 import pyarrow as pa
@@ -102,3 +103,14 @@ def test_polars_conditional(tmp_path):
     actual = vx.open(str(path)).to_polars().filter(expr).collect()
     assert_frame_equal(actual, expected_frame)
     assert actual["id"].to_list() == [1, 2]
+
+
+def test_polars_decimal_literals(tmp_path):
+    frame = pl.DataFrame({"id": [0, 1, 2, 3], "x": [Decimal("1.24"), Decimal("1.25"), None, Decimal("1.26")]})
+    expr = pl.col("x") >= Decimal("1.25")
+    path = tmp_path / "decimal_literals.vortex"
+    vx.io.write(vx.array(frame.to_arrow()), str(path))
+    expected_frame = frame.lazy().filter(expr).collect()
+    actual = vx.open(str(path)).to_polars().filter(expr).collect()
+    assert_frame_equal(actual, expected_frame)
+    assert actual["id"].to_list() == [1, 3]