enh: Deprecate native_namespace in favour of backend in `from_dic…

…t` (#1931)

narwhals/_pandas_like/dataframe.py

@@ -777,16 +777,16 @@ def unique(
     def lazy(self: Self, *, backend: Implementation | None = None) -> CompliantLazyFrame:
         from narwhals.utils import parse_version
 
+        pandas_df = self.to_pandas()
         if backend is None:
             return self
         elif backend is Implementation.DUCKDB:
             import duckdb  # ignore-banned-import
 
             from narwhals._duckdb.dataframe import DuckDBLazyFrame
 
-            df = self._native_frame  # noqa: F841
             return DuckDBLazyFrame(
-                df=duckdb.table("df"),
+                df=duckdb.table("pandas_df"),
                 backend_version=parse_version(duckdb.__version__),
                 version=self._version,
                 validate_column_names=False,
@@ -797,7 +797,7 @@ def lazy(self: Self, *, backend: Implementation | None = None) -> CompliantLazyF
             from narwhals._polars.dataframe import PolarsLazyFrame
 
             return PolarsLazyFrame(
-                df=pl.from_pandas(self._native_frame).lazy(),
+                df=pl.from_pandas(pandas_df).lazy(),
                 backend_version=parse_version(pl.__version__),
                 version=self._version,
             )
@@ -808,7 +808,7 @@ def lazy(self: Self, *, backend: Implementation | None = None) -> CompliantLazyF
             from narwhals._dask.dataframe import DaskLazyFrame
 
             return DaskLazyFrame(
-                native_dataframe=dd.from_pandas(self._native_frame),
+                native_dataframe=dd.from_pandas(pandas_df),
                 backend_version=parse_version(dask.__version__),
                 version=self._version,
                 validate_column_names=False,

narwhals/dataframe.py

@@ -507,7 +507,6 @@ def __arrow_c_stream__(self: Self, requested_schema: object | None = None) -> ob
 
     def lazy(
         self: Self,
-        *,
         backend: ModuleType | Implementation | str | None = None,
     ) -> LazyFrame[Any]:
         """Restrict available API methods to lazy-only ones.

narwhals/functions.py

@@ -28,6 +28,7 @@
 from narwhals.utils import flatten
 from narwhals.utils import parse_version
 from narwhals.utils import validate_laziness
+from narwhals.utils import validate_native_namespace_and_backend
 
 # Missing type parameters for generic type "DataFrame"
 # However, trying to provide one results in mypy still complaining...
@@ -374,6 +375,7 @@ def from_dict(
     data: dict[str, Any],
     schema: dict[str, DType] | Schema | None = None,
     *,
+    backend: ModuleType | Implementation | str | None = None,
     native_namespace: ModuleType | None = None,
 ) -> DataFrame[Any]:
     """Instantiate DataFrame from dictionary.
@@ -388,9 +390,22 @@ def from_dict(
     Arguments:
         data: Dictionary to create DataFrame from.
         schema: The DataFrame schema as Schema or dict of {name: type}.
-        native_namespace: The native library to use for DataFrame creation. Only
+        backend: specifies which eager backend instantiate to. Only
             necessary if inputs are not Narwhals Series.
 
+                `backend` can be specified in various ways:
+
+                - As `Implementation.<BACKEND>` with `BACKEND` being `PANDAS`, `PYARROW`,
+                    `POLARS`, `MODIN` or `CUDF`.
+                - As a string: `"pandas"`, `"pyarrow"`, `"polars"`, `"modin"` or `"cudf"`.
+                - Directly as a module `pandas`, `pyarrow`, `polars`, `modin` or `cudf`.
+        native_namespace: The native library to use for DataFrame creation.
+
+            **Deprecated** (v1.26.0):
+                Please use `backend` instead. Note that `native_namespace` is still available
+                (and won't emit a deprecation warning) if you use `narwhals.stable.v1`,
+                see [perfect backwards compatibility policy](../backcompat.md/).
+
     Returns:
         A new DataFrame.
 
@@ -400,24 +415,20 @@ def from_dict(
         >>> import pyarrow as pa
         >>> import narwhals as nw
         >>> from narwhals.typing import IntoFrameT
-        >>> data = {"a": [1, 2, 3], "b": [4, 5, 6]}
 
-        Let's create a new dataframe of the same class as the dataframe we started with, from a dict of new data:
+        Let's create a new dataframe and specify the backend argument.
 
-        >>> def agnostic_from_dict(df_native: IntoFrameT) -> IntoFrameT:
-        ...     new_data = {"c": [5, 2], "d": [1, 4]}
-        ...     native_namespace = nw.get_native_namespace(df_native)
-        ...     return nw.from_dict(
-        ...         new_data, native_namespace=native_namespace
-        ...     ).to_native()
+        >>> def agnostic_from_dict(backend: str) -> IntoFrameT:
+        ...     data = {"c": [5, 2], "d": [1, 4]}
+        ...     return nw.from_dict(data, backend=backend).to_native()
 
         Let's see what happens when passing pandas, Polars or PyArrow input:
 
-        >>> agnostic_from_dict(pd.DataFrame(data))
+        >>> agnostic_from_dict(backend="pandas")
            c  d
         0  5  1
         1  2  4
-        >>> agnostic_from_dict(pl.DataFrame(data))
+        >>> agnostic_from_dict(backend="polars")
         shape: (2, 2)
         ┌─────┬─────┐
         │ c   ┆ d   │
@@ -427,27 +438,30 @@ def from_dict(
         │ 5   ┆ 1   │
         │ 2   ┆ 4   │
         └─────┴─────┘
-        >>> agnostic_from_dict(pa.table(data))
+        >>> agnostic_from_dict(backend="pyarrow")
         pyarrow.Table
         c: int64
         d: int64
         ----
         c: [[5,2]]
         d: [[1,4]]
     """
+    backend = validate_native_namespace_and_backend(
+        backend, native_namespace, emit_deprecation_warning=True
+    )
     return _from_dict_impl(
         data,
         schema,
-        native_namespace=native_namespace,
+        backend=backend,
         version=Version.MAIN,
     )
 
 
-def _from_dict_impl(
+def _from_dict_impl(  # noqa: PLR0915
     data: dict[str, Any],
     schema: dict[str, DType] | Schema | None = None,
     *,
-    native_namespace: ModuleType | None = None,
+    backend: ModuleType | Implementation | str | None = None,
     version: Version,
 ) -> DataFrame[Any]:
     from narwhals.series import Series
@@ -456,18 +470,31 @@ def _from_dict_impl(
     if not data:
         msg = "from_dict cannot be called with empty dictionary"
         raise ValueError(msg)
-    if native_namespace is None:
+    if backend is None:
         for val in data.values():
             if isinstance(val, Series):
                 native_namespace = val.__native_namespace__()
                 break
         else:
-            msg = "Calling `from_dict` without `native_namespace` is only supported if all input values are already Narwhals Series"
+            msg = "Calling `from_dict` without `backend` is only supported if all input values are already Narwhals Series"
             raise TypeError(msg)
         data = {key: to_native(value, pass_through=True) for key, value in data.items()}
-    implementation = Implementation.from_native_namespace(native_namespace)
+        eager_backend = Implementation.from_native_namespace(native_namespace)
+    else:
+        eager_backend = Implementation.from_backend(backend)
+        native_namespace = eager_backend.to_native_namespace()
 
-    if implementation is Implementation.POLARS:
+    supported_eager_backends = (
+        Implementation.POLARS,
+        Implementation.PANDAS,
+        Implementation.PYARROW,
+        Implementation.MODIN,
+        Implementation.CUDF,
+    )
+    if eager_backend is not None and eager_backend not in supported_eager_backends:
+        msg = f"Unsupported `backend` value.\nExpected one of {supported_eager_backends} or None, got: {eager_backend}."
+        raise ValueError(msg)
+    if eager_backend is Implementation.POLARS:
         if schema:
             from narwhals._polars.utils import (
                 narwhals_to_native_dtype as polars_narwhals_to_native_dtype,
@@ -481,11 +508,11 @@ def _from_dict_impl(
             schema_pl = None
 
         native_frame = native_namespace.from_dict(data, schema=schema_pl)
-    elif implementation in {
+    elif eager_backend in (
         Implementation.PANDAS,
         Implementation.MODIN,
         Implementation.CUDF,
-    }:
+    ):
         aligned_data = {}
         left_most_series = None
         for key, native_series in data.items():
@@ -515,16 +542,16 @@ def _from_dict_impl(
             schema = {
                 name: pandas_like_narwhals_to_native_dtype(
                     dtype=schema[name],
-                    dtype_backend=get_dtype_backend(native_type, implementation),
-                    implementation=implementation,
+                    dtype_backend=get_dtype_backend(native_type, eager_backend),
+                    implementation=eager_backend,
                     backend_version=backend_version,
                     version=version,
                 )
                 for name, native_type in native_frame.dtypes.items()
             }
             native_frame = native_frame.astype(schema)
 
-    elif implementation is Implementation.PYARROW:
+    elif eager_backend is Implementation.PYARROW:
         if schema:
             from narwhals._arrow.utils import (
                 narwhals_to_native_dtype as arrow_narwhals_to_native_dtype,

narwhals/stable/v1/__init__.py

@@ -78,6 +78,7 @@
 from narwhals.utils import maybe_get_index
 from narwhals.utils import maybe_reset_index
 from narwhals.utils import maybe_set_index
+from narwhals.utils import validate_native_namespace_and_backend
 from narwhals.utils import validate_strict_and_pass_though
 
 if TYPE_CHECKING:
@@ -169,7 +170,6 @@ def __getitem__(self: Self, item: Any) -> Any:
 
     def lazy(
         self: Self,
-        *,
         backend: ModuleType | Implementation | str | None = None,
     ) -> LazyFrame[Any]:
         """Restrict available API methods to lazy-only ones.
@@ -2162,6 +2162,7 @@ def from_dict(
     data: dict[str, Any],
     schema: dict[str, DType] | Schema | None = None,
     *,
+    backend: ModuleType | Implementation | str | None = None,
     native_namespace: ModuleType | None = None,
 ) -> DataFrame[Any]:
     """Instantiate DataFrame from dictionary.
@@ -2176,17 +2177,33 @@ def from_dict(
     Arguments:
         data: Dictionary to create DataFrame from.
         schema: The DataFrame schema as Schema or dict of {name: type}.
-        native_namespace: The native library to use for DataFrame creation. Only
+        backend: specifies which eager backend instantiate to. Only
             necessary if inputs are not Narwhals Series.
 
+                `backend` can be specified in various ways:
+
+                - As `Implementation.<BACKEND>` with `BACKEND` being `PANDAS`, `PYARROW`,
+                    `POLARS`, `MODIN` or `CUDF`.
+                - As a string: `"pandas"`, `"pyarrow"`, `"polars"`, `"modin"` or `"cudf"`.
+                - Directly as a module `pandas`, `pyarrow`, `polars`, `modin` or `cudf`.
+        native_namespace: The native library to use for DataFrame creation.
+
+            **Deprecated** (v1.26.0):
+                Please use `backend` instead. Note that `native_namespace` is still available
+                (and won't emit a deprecation warning) if you use `narwhals.stable.v1`,
+                see [perfect backwards compatibility policy](../backcompat.md/).
+
     Returns:
         A new DataFrame.
     """
+    backend = validate_native_namespace_and_backend(
+        backend, native_namespace, emit_deprecation_warning=False
+    )
     return _stableify(  # type: ignore[no-any-return]
         _from_dict_impl(
             data,
             schema,
-            native_namespace=native_namespace,
+            backend=backend,
             version=Version.V1,
         )
     )

narwhals/utils.py

@@ -162,16 +162,41 @@ def to_native_namespace(self: Self) -> ModuleType:
         Returns:
             Native module.
         """
-        mapping = {
-            Implementation.PANDAS: get_pandas(),
-            Implementation.MODIN: get_modin(),
-            Implementation.CUDF: get_cudf(),
-            Implementation.PYARROW: get_pyarrow(),
-            Implementation.PYSPARK: get_pyspark_sql(),
-            Implementation.POLARS: get_polars(),
-            Implementation.DASK: get_dask_dataframe(),
-        }
-        return mapping[self]  # type: ignore[no-any-return]
+        if self is Implementation.PANDAS:
+            import pandas as pd  # ignore-banned-import
+
+            return pd  # type: ignore[no-any-return]
+        if self is Implementation.MODIN:
+            import modin.pandas
+
+            return modin.pandas  # type: ignore[no-any-return]
+        if self is Implementation.CUDF:  # pragma: no cover
+            import cudf  # ignore-banned-import
+
+            return cudf  # type: ignore[no-any-return]
+        if self is Implementation.PYARROW:
+            import pyarrow as pa  # ignore-banned-import
+
+            return pa  # type: ignore[no-any-return]
+        if self is Implementation.PYSPARK:  # pragma: no cover
+            import pyspark.sql
+
+            return pyspark.sql  # type: ignore[no-any-return]
+        if self is Implementation.POLARS:
+            import polars as pl  # ignore-banned-import
+
+            return pl
+        if self is Implementation.DASK:
+            import dask.dataframe  # ignore-banned-import
+
+            return dask.dataframe  # type: ignore[no-any-return]
+
+        if self is Implementation.DUCKDB:
+            import duckdb  # ignore-banned-import
+
+            return duckdb  # type: ignore[no-any-return]
+        msg = "Not supported Implementation"  # pragma: no cover
+        raise AssertionError(msg)
 
     def is_pandas(self: Self) -> bool:
         """Return whether implementation is pandas.
@@ -1042,6 +1067,27 @@ def validate_strict_and_pass_though(
     return pass_through
 
 
+def validate_native_namespace_and_backend(
+    backend: ModuleType | Implementation | str | None = None,
+    native_namespace: ModuleType | None = None,
+    *,
+    emit_deprecation_warning: bool,
+) -> ModuleType | Implementation | str | None:
+    if native_namespace is not None and backend is None:  # pragma: no cover
+        if emit_deprecation_warning:
+            msg = (
+                "`native_namespace` is deprecated, please use `pass_through` instead.\n\n"
+                "Note: `native_namespace` will remain available in `narwhals.stable.v1`.\n"
+                "See https://narwhals-dev.github.io/narwhals/backcompat/ for more information.\n"
+            )
+            issue_deprecation_warning(msg, _version="1.25.1")
+        backend = native_namespace
+    elif native_namespace is not None and backend is not None:
+        msg = "Can't pass both `native_namespace` and `backend`"
+        raise ValueError(msg)
+    return backend
+
+
 def _validate_rolling_arguments(
     window_size: int, min_samples: int | None
 ) -> tuple[int, int]:

tests/frame/lazy_test.py

@@ -56,12 +56,9 @@ def test_lazy_to_default(constructor_eager: ConstructorEager) -> None:
     ],
 )
 def test_lazy_backend(
-    request: pytest.FixtureRequest,
     constructor_eager: ConstructorEager,
     backend: Implementation | str,
 ) -> None:
-    if "modin" in str(constructor_eager):
-        request.applymarker(pytest.mark.xfail)
     if (backend is Implementation.DASK) or backend == "dask":
         pytest.importorskip("dask")
     if (backend is Implementation.DUCKDB) or backend == "duckdb":