feat: add to_lowercase and to_uppercase to duckdb

narwhals/_duckdb/expr.py

@@ -370,7 +370,7 @@ def is_between(
         closed: Literal["left", "right", "none", "both"],
     ) -> Self:
         def func(
-            _input: duckdb.Expression, lower_bound, upper_bound
+            _input: duckdb.Expression, lower_bound: Any, upper_bound: Any
         ) -> duckdb.Expression:
             if closed == "left":
                 return (_input >= lower_bound) & (_input < upper_bound)
@@ -573,6 +573,24 @@ def func(_input: duckdb.Expression) -> duckdb.Expression:
             returns_scalar=False,
         )
 
+    def to_lowercase(self) -> DuckDBExpr:
+        from duckdb import FunctionExpression
+
+        return self._compliant_expr._from_call(
+            lambda _input: FunctionExpression("lower", _input),
+            "to_lowercase",
+            returns_scalar=False,
+        )
+
+    def to_uppercase(self) -> DuckDBExpr:
+        from duckdb import FunctionExpression
+
+        return self._compliant_expr._from_call(
+            lambda _input: FunctionExpression("upper", _input),
+            "to_uppercase",
+            returns_scalar=False,
+        )
+
 
 class DuckDBExprDateTimeNamespace:
     def __init__(self, expr: DuckDBExpr) -> None:

tests/expr_and_series/str/to_uppercase_to_lowercase_test.py

@@ -39,6 +39,7 @@ def test_str_to_uppercase(
             "pandas_pyarrow_constructor",
             "pyarrow_table_constructor",
             "modin_constructor",
+            "duckdb_lazy_constructor",
         )
         or ("dask" in str(constructor) and PYARROW_VERSION >= (12,))
     ):
@@ -80,6 +81,7 @@ def test_str_to_uppercase_series(
             "pandas_nullable_constructor",
             "polars_eager_constructor",
             "cudf_constructor",
+            "duckdb_lazy_constructor",
         )
     ):
         # We are marking it xfail for these conditions above