typing

xarray/core/groupby.py

@@ -1357,7 +1357,12 @@ def where(self, cond, other=dtypes.NA) -> T_Xarray:
         """
         return ops.where_method(self, cond, other)
 
-    def _first_or_last(self, op: str, skipna: bool | None, keep_attrs: bool | None):
+    def _first_or_last(
+        self,
+        op: Literal["first" | "last"],
+        skipna: bool | None,
+        keep_attrs: bool | None,
+    ):
         if all(
             isinstance(maybe_slice, slice)
             and (maybe_slice.stop == maybe_slice.start + 1)
@@ -1369,13 +1374,12 @@ def _first_or_last(self, op: str, skipna: bool | None, keep_attrs: bool | None):
         if keep_attrs is None:
             keep_attrs = _get_keep_attrs(default=True)
         if (
-            skipna
-            and module_available("flox", minversion="0.9.16")
+            module_available("flox", minversion="0.9.16")
             and OPTIONS["use_flox"]
             and contains_only_chunked_or_numpy(self._obj)
         ):
             result, *_ = self._flox_reduce(
-                dim=None, func=f"nan{op}" if skipna else op, keep_attrs=keep_attrs
+                dim=None, func=op, skipna=skipna, keep_attrs=keep_attrs
             )
         else:
             result = self.reduce(