fix: cuDF compat (#794)

narwhals/_pandas_like/dataframe.py

@@ -219,7 +219,7 @@ def select(
     ) -> Self:
         if exprs and all(isinstance(x, str) for x in exprs) and not named_exprs:
             # This is a simple slice => fastpath!
-            return self._from_native_frame(self._native_frame.loc[:, exprs])
+            return self._from_native_frame(self._native_frame.loc[:, list(exprs)])
         new_series = evaluate_into_exprs(self, *exprs, **named_exprs)
         if not new_series:
             # return empty dataframe, like Polars does

narwhals/_pandas_like/utils.py

@@ -282,7 +282,20 @@ def translate_dtype(column: Any) -> DType:
             # which is inferred by default.
             return dtypes.String()
         else:
-            return dtypes.Object()
+            df = column.to_frame()
+            if hasattr(df, "__dataframe__"):
+                from narwhals._interchange.dataframe import (
+                    map_interchange_dtype_to_narwhals_dtype,
+                )
+
+                try:
+                    return map_interchange_dtype_to_narwhals_dtype(
+                        df.__dataframe__().get_column(0).dtype
+                    )
+                except Exception:  # noqa: BLE001
+                    return dtypes.Object()
+            else:  # pragma: no cover
+                return dtypes.Object()
     return dtypes.Unknown()
 
 

tests/frame/schema_test.py

@@ -45,7 +45,9 @@ def test_schema_comparison() -> None:
 
 
 def test_object() -> None:
-    df = pd.DataFrame({"a": [1, 2, 3]}).astype(object)
+    class Foo: ...
+
+    df = pd.DataFrame({"a": [Foo()]}).astype(object)
     result = nw.from_native(df).schema
     assert result["a"] == nw.Object
 
@@ -57,7 +59,7 @@ def test_string_disguised_as_object() -> None:
 
 
 def test_actual_object(request: Any, constructor_eager: Any) -> None:
-    if "pyarrow_table" in str(constructor_eager):
+    if any(x in str(constructor_eager) for x in ("modin", "pyarrow_table")):
         request.applymarker(pytest.mark.xfail)
 
     class Foo: ...