refactor(pkg-py): remove unused duckdb_result_to_nw function

The function is no longer used since DataFrameSource now uses
duckdb_result_to_polars and duckdb_result_to_pandas directly.
Updated tests to use duckdb_result_to_polars.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: cpsievert

pkg-py/src/querychat/_df_compat.py

@@ -57,30 +57,6 @@ def read_sql_pyarrow(query: TextClause, conn: Connection):
     return pl.read_database(query, connection=conn).to_arrow()
 
 
-def duckdb_result_to_nw(
-    result: duckdb.DuckDBPyRelation | duckdb.DuckDBPyConnection,
-) -> nw.DataFrame:
-    # Check for polars first without consuming the result
-    try:
-        import polars  # noqa: F401, ICN001  # pyright: ignore[reportMissingImports]
-
-        return nw.from_native(result.pl())
-    except ImportError:
-        pass
-    except Exception:  # noqa: S110
-        # Other polars errors (e.g., missing pyarrow) - fall through to pandas
-        pass
-
-    try:
-        import pandas  # noqa: F401, ICN001  # pyright: ignore[reportMissingImports]
-
-        return nw.from_native(result.df())
-    except ImportError:
-        pass
-
-    raise ImportError(f"DataFrameSource requires 'polars' or 'pandas'. {_INSTALL_MSG}")
-
-
 def duckdb_result_to_polars(
     result: duckdb.DuckDBPyRelation | duckdb.DuckDBPyConnection,
 ):

pkg-py/tests/test_df_compat.py

@@ -7,7 +7,7 @@
 import duckdb
 import narwhals.stable.v1 as nw
 import pytest
-from querychat._df_compat import duckdb_result_to_nw, read_csv
+from querychat._df_compat import duckdb_result_to_polars, read_csv
 
 # Check if polars and pyarrow are available (both needed for DuckDB + polars)
 try:
@@ -60,8 +60,11 @@ def test_read_csv_data_integrity(self, gzip_csv_file):
         assert names == ["Alice", "Bob", "Charlie"]
 
 
-class TestDuckdbResultToNw:
-    """Tests for the duckdb_result_to_nw function."""
+@pytest.mark.skipif(
+    not HAS_POLARS_WITH_PYARROW, reason="polars or pyarrow not installed"
+)
+class TestDuckdbResultToPolars:
+    """Tests for the duckdb_result_to_polars function."""
 
     @pytest.fixture
     def duckdb_conn(self):
@@ -73,16 +76,16 @@ def duckdb_conn(self):
         yield conn
         conn.close()
 
-    def test_duckdb_result_returns_narwhals_dataframe(self, duckdb_conn):
-        """Test that duckdb_result_to_nw returns a narwhals DataFrame."""
+    def test_duckdb_result_returns_polars_dataframe(self, duckdb_conn):
+        """Test that duckdb_result_to_polars returns a polars DataFrame."""
         result = duckdb_conn.execute("SELECT * FROM test")
-        df = duckdb_result_to_nw(result)
-        assert isinstance(df, nw.DataFrame)
+        df = duckdb_result_to_polars(result)
+        assert isinstance(df, pl.DataFrame)
 
     def test_duckdb_result_has_correct_data(self, duckdb_conn):
-        """Test that duckdb_result_to_nw preserves data correctly."""
+        """Test that duckdb_result_to_polars preserves data correctly."""
         result = duckdb_conn.execute("SELECT * FROM test ORDER BY id")
-        df = duckdb_result_to_nw(result)
+        df = duckdb_result_to_polars(result)
 
         assert df.shape == (2, 3)
         assert list(df.columns) == ["id", "name", "value"]
@@ -92,9 +95,9 @@ def test_duckdb_result_has_correct_data(self, duckdb_conn):
     def test_duckdb_result_empty_query(self, duckdb_conn):
         """Test handling of empty query results."""
         result = duckdb_conn.execute("SELECT * FROM test WHERE id > 100")
-        df = duckdb_result_to_nw(result)
+        df = duckdb_result_to_polars(result)
 
-        assert isinstance(df, nw.DataFrame)
+        assert isinstance(df, pl.DataFrame)
         assert df.shape == (0, 3)
 
 
@@ -117,18 +120,3 @@ def test_read_csv_uses_polars_when_available(self):
             assert isinstance(native, pl.DataFrame)
         finally:
             Path(temp_path).unlink()
-
-    def test_duckdb_result_uses_polars_when_available(self):
-        """Test that duckdb_result_to_nw uses polars when available."""
-        conn = duckdb.connect(":memory:")
-        conn.execute("CREATE TABLE t (x INTEGER)")
-        conn.execute("INSERT INTO t VALUES (1)")
-
-        result = conn.execute("SELECT * FROM t")
-        df = duckdb_result_to_nw(result)
-
-        # The native frame should be polars when polars is available
-        native = df.to_native()
-        assert isinstance(native, pl.DataFrame)
-
-        conn.close()