fix fallback isdtype method (#9250)

xarray/core/npcompat.py

@@ -28,14 +28,18 @@
 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+from __future__ import annotations
+
+from typing import Any
 
 try:
     # requires numpy>=2.0
     from numpy import isdtype  # type: ignore[attr-defined,unused-ignore]
 except ImportError:
     import numpy as np
+    from numpy.typing import DTypeLike
 
-    dtype_kinds = {
+    kind_mapping = {
         "bool": np.bool_,
         "signed integer": np.signedinteger,
         "unsigned integer": np.unsignedinteger,
@@ -45,16 +49,25 @@
         "numeric": np.number,
     }
 
-    def isdtype(dtype, kind):
+    def isdtype(
+        dtype: np.dtype[Any] | type[Any], kind: DTypeLike | tuple[DTypeLike, ...]
+    ) -> bool:
         kinds = kind if isinstance(kind, tuple) else (kind,)
+        str_kinds = {k for k in kinds if isinstance(k, str)}
+        type_kinds = {k.type for k in kinds if isinstance(k, np.dtype)}
 
-        unknown_dtypes = [kind for kind in kinds if kind not in dtype_kinds]
-        if unknown_dtypes:
-            raise ValueError(f"unknown dtype kinds: {unknown_dtypes}")
+        if unknown_kind_types := set(kinds) - str_kinds - type_kinds:
+            raise TypeError(
+                f"kind must be str, np.dtype or a tuple of these, got {unknown_kind_types}"
+            )
+        if unknown_kinds := {k for k in str_kinds if k not in kind_mapping}:
+            raise ValueError(
+                f"unknown kind: {unknown_kinds}, must be a np.dtype or one of {list(kind_mapping)}"
+            )
 
         # verified the dtypes already, no need to check again
-        translated_kinds = [dtype_kinds[kind] for kind in kinds]
+        translated_kinds = {kind_mapping[k] for k in str_kinds} | type_kinds
         if isinstance(dtype, np.generic):
-            return any(isinstance(dtype, kind) for kind in translated_kinds)
+            return isinstance(dtype, translated_kinds)
         else:
-            return any(np.issubdtype(dtype, kind) for kind in translated_kinds)
+            return any(np.issubdtype(dtype, k) for k in translated_kinds)