fix: add native_namespace to interchange level of support

Author: FBruzzesi

narwhals/_duckdb/dataframe.py

@@ -4,9 +4,12 @@
 from typing import TYPE_CHECKING
 from typing import Any
 
+from narwhals.dependencies import get_duckdb
 from narwhals.utils import parse_version
 
 if TYPE_CHECKING:
+    from types import ModuleType
+
     import pandas as pd
     import pyarrow as pa
     from typing_extensions import Self
@@ -68,6 +71,9 @@ def __init__(self, df: Any, dtypes: DTypes) -> None:
     def __narwhals_dataframe__(self) -> Any:
         return self
 
+    def __native_namespace__(self: Self) -> ModuleType:
+        return get_duckdb()  # type: ignore[no-any-return]
+
     def __getitem__(self, item: str) -> DuckDBInterchangeSeries:
         from narwhals._duckdb.series import DuckDBInterchangeSeries
 

narwhals/_duckdb/series.py

@@ -4,8 +4,11 @@
 from typing import Any
 
 from narwhals._duckdb.dataframe import map_duckdb_dtype_to_narwhals_dtype
+from narwhals.dependencies import get_duckdb
 
 if TYPE_CHECKING:
+    from types import ModuleType
+
     from narwhals.typing import DTypes
 
 
@@ -17,6 +20,9 @@ def __init__(self, df: Any, dtypes: DTypes) -> None:
     def __narwhals_series__(self) -> Any:
         return self
 
+    def __native_namespace__(self) -> ModuleType:
+        return get_duckdb()  # type: ignore[no-any-return]
+
     def __getattr__(self, attr: str) -> Any:
         if attr == "dtype":
             return map_duckdb_dtype_to_narwhals_dtype(

narwhals/_ibis/dataframe.py

@@ -3,7 +3,11 @@
 from typing import TYPE_CHECKING
 from typing import Any
 
+from narwhals.dependencies import get_ibis
+
 if TYPE_CHECKING:
+    from types import ModuleType
+
     import pandas as pd
     import pyarrow as pa
     from typing_extensions import Self
@@ -59,6 +63,9 @@ def __init__(self, df: Any, dtypes: DTypes) -> None:
     def __narwhals_dataframe__(self) -> Any:
         return self
 
+    def __native_namespace__(self: Self) -> ModuleType:
+        return get_ibis()  # type: ignore[no-any-return]
+
     def __getitem__(self, item: str) -> IbisInterchangeSeries:
         from narwhals._ibis.series import IbisInterchangeSeries
 

narwhals/_ibis/series.py

@@ -4,8 +4,11 @@
 from typing import Any
 
 from narwhals._ibis.dataframe import map_ibis_dtype_to_narwhals_dtype
+from narwhals.dependencies import get_ibis
 
 if TYPE_CHECKING:
+    from types import ModuleType
+
     from narwhals.typing import DTypes
 
 
@@ -17,6 +20,9 @@ def __init__(self, df: Any, dtypes: DTypes) -> None:
     def __narwhals_series__(self) -> Any:
         return self
 
+    def __native_namespace__(self) -> ModuleType:
+        return get_ibis()  # type: ignore[no-any-return]
+
     def __getattr__(self, attr: str) -> Any:
         if attr == "dtype":
             return map_ibis_dtype_to_narwhals_dtype(

narwhals/_interchange/dataframe.py

@@ -82,6 +82,14 @@ def __init__(self, df: Any, dtypes: DTypes) -> None:
     def __narwhals_dataframe__(self) -> Any:
         return self
 
+    def __native_namespace__(self: Self) -> NoReturn:
+        msg = (
+            "Cannot access native namespace for metadata-only dataframes with unknown backend."
+            "If you would like to see this kind of object supported in Narwhals, please "
+            "open a feature request at https://github.com/narwhals-dev/narwhals/issues."
+        )
+        raise NotImplementedError(msg)
+
     def __getitem__(self, item: str) -> InterchangeSeries:
         from narwhals._interchange.series import InterchangeSeries
 

narwhals/_interchange/series.py

@@ -2,6 +2,7 @@
 
 from typing import TYPE_CHECKING
 from typing import Any
+from typing import NoReturn
 
 from narwhals._interchange.dataframe import map_interchange_dtype_to_narwhals_dtype
 
@@ -17,6 +18,14 @@ def __init__(self, df: Any, dtypes: DTypes) -> None:
     def __narwhals_series__(self) -> Any:
         return self
 
+    def __native_namespace__(self) -> NoReturn:
+        msg = (
+            "Cannot access native namespace for metadata-only series with unknown backend. "
+            "If you would like to see this kind of object supported in Narwhals, please "
+            "open a feature request at https://github.com/narwhals-dev/narwhals/issues."
+        )
+        raise NotImplementedError(msg)
+
     def __getattr__(self, attr: str) -> Any:
         if attr == "dtype":
             return map_interchange_dtype_to_narwhals_dtype(

tests/frame/interchange_native_namespace_test.py

@@ -0,0 +1,52 @@
+import duckdb
+import polars as pl
+import pytest
+
+import narwhals.stable.v1 as nw
+
+data = {"a": [1, 2, 3], "b": [4.5, 6.7, 8.9], "z": ["x", "y", "w"]}
+
+
+def test_interchange() -> None:
+    df_pl = pl.DataFrame(data)
+    df = nw.from_native(df_pl.__dataframe__(), eager_or_interchange_only=True)
+    series = df["a"]
+
+    with pytest.raises(
+        NotImplementedError,
+        match="Cannot access native namespace for metadata-only dataframes with unknown backend",
+    ):
+        df.__native_namespace__()
+
+    with pytest.raises(
+        NotImplementedError,
+        match="Cannot access native namespace for metadata-only series with unknown backend",
+    ):
+        series.__native_namespace__()
+
+
+def test_ibis(
+    tmpdir: pytest.TempdirFactory,
+) -> None:  # pragma: no cover
+    ibis = pytest.importorskip("ibis")
+    df_pl = pl.DataFrame(data)
+
+    filepath = str(tmpdir / "file.parquet")  # type: ignore[operator]
+    df_pl.write_parquet(filepath)
+    tbl = ibis.read_parquet(filepath)
+    df = nw.from_native(tbl, eager_or_interchange_only=True)
+    series = df["a"]
+
+    assert df.__native_namespace__() == ibis
+    assert series.__native_namespace__() == ibis
+
+
+def test_duckdb() -> None:
+    df_pl = pl.DataFrame(data)  # noqa: F841
+
+    rel = duckdb.sql("select * from df_pl")
+    df = nw.from_native(rel, eager_or_interchange_only=True)
+    series = df["a"]
+
+    assert df.__native_namespace__() == duckdb
+    assert series.__native_namespace__() == duckdb