feat: add native property and deprecate .to_native() method

docs/api-reference/dataframe.md

@@ -24,6 +24,7 @@
         - join
         - join_asof
         - lazy
+        - native
         - null_count
         - pipe
         - rename

docs/api-reference/lazyframe.md

@@ -18,6 +18,7 @@
         - join_asof
         - lazy
         - pipe
+        - native
         - rename
         - schema
         - select

docs/api-reference/series.md

@@ -39,6 +39,7 @@
         - min
         - mode
         - name
+        - native
         - n_unique
         - null_count
         - pipe

narwhals/dataframe.py

@@ -328,6 +328,11 @@ def _series(self) -> type[Series]:
     def _lazyframe(self) -> type[LazyFrame[Any]]:
         return LazyFrame
 
+    @property
+    def native(self: Self) -> DataFrameT:
+        """Returns native frame underlying Narwhals DataFrame."""
+        return self._compliant_frame._native_frame  # type: ignore[no-any-return]
+
     def __init__(
         self,
         df: Any,
@@ -2765,6 +2770,11 @@ class LazyFrame(BaseFrame[FrameT]):
     def _dataframe(self) -> type[DataFrame[Any]]:
         return DataFrame
 
+    @property
+    def native(self: Self) -> FrameT:
+        """Returns native frame underlying Narwhals LazyFrame."""
+        return self._compliant_frame._native_frame  # type: ignore[no-any-return]
+
     def __init__(
         self,
         df: Any,

narwhals/series.py

@@ -41,6 +41,11 @@ def _dataframe(self) -> type[DataFrame[Any]]:
 
         return DataFrame
 
+    @property
+    def native(self: Self) -> Any:
+        """Returns native series underlying Narwhals Series."""
+        return self._compliant_series._native_series
+
     def __init__(
         self: Self,
         series: Any,

tests/frame/to_native_test.py

@@ -14,3 +14,4 @@ def test_to_native(constructor: Constructor) -> None:
     df = nw.from_native(df_raw)
 
     assert isinstance(df.to_native(), df_raw.__class__)
+    assert isinstance(df.native, df_raw.__class__)

tests/series_only/to_native_test.py

@@ -13,5 +13,5 @@
 def test_to_native(constructor_eager: ConstructorEager) -> None:
     orig_series = constructor_eager({"a": data})["a"]  # type: ignore[index]
     nw_series = nw.from_native(constructor_eager({"a": data}), eager_only=True)["a"]
-    result = nw_series.to_native()
-    assert isinstance(result, orig_series.__class__)
+    assert isinstance(nw_series.to_native(), orig_series.__class__)
+    assert isinstance(nw_series.native, orig_series.__class__)

utils/check_api_reference.py

@@ -19,6 +19,7 @@
     "is_sorted",
     "item",
     "name",
+    "native",
     "rename",
     "scatter",
     "shape",