feat: support to_list for cudf, note limitations (#1335)

* feat: support to_list for cudf, note limitations

* feat: support to_list for cudf, note limitations

Author: MarcoGorelli

narwhals/_pandas_like/dataframe.py

@@ -280,7 +280,7 @@ def rows(
     ) -> list[tuple[Any, ...]] | list[dict[str, Any]]:
         if not named:
             # cuDF does not support itertuples. But it does support to_dict!
-            if self._implementation is Implementation.CUDF:  # pragma: no cover
+            if self._implementation is Implementation.CUDF:
                 # Extract the row values from the named rows
                 return [tuple(row.values()) for row in self.rows(named=True)]
 
@@ -532,7 +532,7 @@ def join(
                 )
 
         if how == "anti":
-            if self._implementation is Implementation.CUDF:  # pragma: no cover
+            if self._implementation is Implementation.CUDF:
                 return self._from_native_frame(
                     self._native_frame.merge(
                         other._native_frame,
@@ -730,7 +730,7 @@ def to_numpy(self, dtype: Any = None, copy: bool | None = None) -> Any:
     def to_pandas(self) -> Any:
         if self._implementation is Implementation.PANDAS:
             return self._native_frame
-        if self._implementation is Implementation.MODIN:  # pragma: no cover
+        if self._implementation is Implementation.MODIN:
             return self._native_frame._to_pandas()
         return self._native_frame.to_pandas()  # pragma: no cover
 
@@ -797,7 +797,7 @@ def gather_every(self: Self, n: int, offset: int = 0) -> Self:
         return self._from_native_frame(self._native_frame.iloc[offset::n])
 
     def to_arrow(self: Self) -> Any:
-        if self._implementation is Implementation.CUDF:  # pragma: no cover
+        if self._implementation is Implementation.CUDF:
             return self._native_frame.to_arrow(preserve_index=False)
 
         import pyarrow as pa  # ignore-banned-import()

narwhals/_pandas_like/series.py

@@ -223,6 +223,8 @@ def to_frame(self) -> PandasLikeDataFrame:
         )
 
     def to_list(self) -> Any:
+        if self._implementation is Implementation.CUDF:
+            return self._native_series.to_arrow().to_pylist()
         return self._native_series.to_list()
 
     def is_between(
@@ -544,9 +546,9 @@ def to_numpy(self, dtype: Any = None, copy: bool | None = None) -> Any:
     def to_pandas(self) -> Any:
         if self._implementation is Implementation.PANDAS:
             return self._native_series
-        elif self._implementation is Implementation.CUDF:  # pragma: no cover
+        elif self._implementation is Implementation.CUDF:
             return self._native_series.to_pandas()
-        elif self._implementation is Implementation.MODIN:  # pragma: no cover
+        elif self._implementation is Implementation.MODIN:
             return self._native_series._to_pandas()
         msg = f"Unknown implementation: {self._implementation}"  # pragma: no cover
         raise AssertionError(msg)
@@ -671,7 +673,7 @@ def clip(
         )
 
     def to_arrow(self: Self) -> Any:
-        if self._implementation is Implementation.CUDF:  # pragma: no cover
+        if self._implementation is Implementation.CUDF:
             return self._native_series.to_arrow()
 
         import pyarrow as pa  # ignore-banned-import()

narwhals/series.py

@@ -468,6 +468,12 @@ def to_list(self) -> list[Any]:
         """
         Convert to list.
 
+        Notes:
+            This function converts to Python scalars. It's typically
+            more efficient to keep your data in the format native to
+            your original dataframe, so we recommend only calling this
+            when you absolutely need to.
+
         Examples:
             >>> import pandas as pd
             >>> import polars as pl

pyproject.toml

@@ -138,8 +138,8 @@ omit = [
 exclude_also = [
   "> POLARS_VERSION",
   "if sys.version_info() <",
-  "if implementation is Implementation.MODIN",
-  "if implementation is Implementation.CUDF",
+  "if (:?self._)?implementation is Implementation.MODIN",
+  "if (:?self._)?implementation is Implementation.CUDF",
   'request.applymarker\(pytest.mark.xfail\)'
 ]