test columns with spaces

narwhals/_duckdb/dataframe.py

@@ -326,7 +326,13 @@ def drop_nulls(self: Self, subset: str | list[str] | None) -> Self:
         import duckdb
 
         rel = self._native_frame
-        subset_ = subset if subset is not None else rel.columns
-        keep_condition = " and ".join(f"{col} is not null" for col in subset_)
+        subset_ = (
+            [subset]
+            if isinstance(subset, str)
+            else rel.columns
+            if subset is None
+            else subset
+        )
+        keep_condition = " and ".join(f'"{col}" is not null' for col in subset_)
         query = f"""select * from rel where {keep_condition}"""  # noqa: S608
         return self._from_native_frame(duckdb.sql(query))

tests/frame/drop_nulls_test.py

@@ -7,26 +7,26 @@
 from tests.utils import assert_equal_data
 
 data = {
-    "a": [1.0, 2.0, None, 4.0],
-    "b": [None, 3.0, None, 5.0],
+    "alpha": [1.0, 2.0, None, 4.0],
+    "beta gamma": [None, 3.0, None, 5.0],
 }
 
 
 def test_drop_nulls(constructor: Constructor) -> None:
     result = nw.from_native(constructor(data)).drop_nulls()
     expected = {
-        "a": [2.0, 4.0],
-        "b": [3.0, 5.0],
+        "alpha": [2.0, 4.0],
+        "beta gamma": [3.0, 5.0],
     }
     assert_equal_data(result, expected)
 
 
 @pytest.mark.parametrize(
     ("subset", "expected"),
     [
-        ("a", {"a": [1, 2.0, 4.0], "b": [None, 3.0, 5.0]}),
-        (["a"], {"a": [1, 2.0, 4.0], "b": [None, 3.0, 5.0]}),
-        (["a", "b"], {"a": [2.0, 4.0], "b": [3.0, 5.0]}),
+        ("alpha", {"alpha": [1, 2.0, 4.0], "beta gamma": [None, 3.0, 5.0]}),
+        (["alpha"], {"alpha": [1, 2.0, 4.0], "beta gamma": [None, 3.0, 5.0]}),
+        (["alpha", "beta gamma"], {"alpha": [2.0, 4.0], "beta gamma": [3.0, 5.0]}),
     ],
 )
 def test_drop_nulls_subset(