feat: Add is_boolean method to DType. (#2935)

Author: kklein

narwhals/dtypes.py

@@ -95,6 +95,10 @@ def is_temporal(cls: type[Self]) -> bool:
     def is_nested(cls: type[Self]) -> bool:
         return issubclass(cls, NestedType)
 
+    @classmethod
+    def is_boolean(cls: type[Self]) -> bool:
+        return issubclass(cls, Boolean)
+
     def __eq__(self, other: DType | type[DType]) -> bool:  # type: ignore[override]
         from narwhals._utils import isinstance_or_issubclass
 

tests/dtypes_test.py

@@ -315,6 +315,7 @@ def test_dtype_is_x() -> None:
     is_decimal = {nw.Decimal}
     is_temporal = {nw.Datetime, nw.Date, nw.Duration, nw.Time}
     is_nested = {nw.Array, nw.List, nw.Struct}
+    is_boolean = {nw.Boolean}
 
     for dtype in dtypes:
         assert dtype.is_numeric() == (
@@ -332,6 +333,7 @@ def test_dtype_is_x() -> None:
         assert dtype.is_decimal() == (dtype in is_decimal)
         assert dtype.is_temporal() == (dtype in is_temporal)
         assert dtype.is_nested() == (dtype in is_nested)
+        assert dtype.is_boolean() == (dtype in is_boolean)
 
 
 @pytest.mark.skipif(POLARS_VERSION < (1, 18), reason="too old for Int128")