Fix sortby raising KeyError when passed a tuple of dimension names

doc/whats-new.rst

@@ -162,6 +162,9 @@ Deprecations
 Bug Fixes
 ~~~~~~~~~
 
+- Fix :py:meth:`DataArray.sortby` and :py:meth:`Dataset.sortby` raising ``KeyError``
+  when passing a tuple of dimension names, e.g. ``da.sortby(da.dims)`` (:issue:`4821`).
+  By `Timothy Hodson <https://github.com/thodson-usgs>`_.
 - Fix multi-coordinate indexes being dropped in :py:meth:`DataArray._replace_maybe_drop_dims`
   (e.g. after reducing over an unrelated dimension) and in :py:meth:`Dataset._copy_listed`
   (e.g. when subsetting a Dataset by variable names). Both paths now consult

xarray/core/dataset.py

@@ -8149,8 +8149,12 @@ def sortby(
 
         if callable(variables):
             variables = variables(self)
-        if not isinstance(variables, list):
+        if isinstance(variables, (str, DataArray)) or not isinstance(
+            variables, Iterable
+        ):
             variables = [variables]
+        else:
+            variables = list(variables)
         arrays = [v if isinstance(v, DataArray) else self[v] for v in variables]
         aligned_vars = align(self, *arrays, join="left")
         aligned_self = cast("Self", aligned_vars[0])

xarray/tests/test_dataarray.py

@@ -4558,6 +4558,11 @@ def test_sortby(self) -> None:
         actual = da.sortby(["x", "y"])
         assert_equal(actual, expected)
 
+        # test tuple of dimension names (GH4821)
+        expected = sorted2d
+        actual = da.sortby(("x", "y"))
+        assert_equal(actual, expected)
+
     @requires_bottleneck
     def test_rank(self) -> None:
         # floats

xarray/tests/test_dataset.py

@@ -7323,6 +7323,11 @@ def test_sortby(self) -> None:
         actual = ds.sortby(["x", "y"], ascending=False)
         assert_equal(actual, ds)
 
+        # test tuple of dimension names (GH4821)
+        expected = sorted2d
+        actual = ds.sortby(("x", "y"))
+        assert_equal(actual, expected)
+
     def test_sortby_descending_nans(self) -> None:
         # Regression test for https://github.com/pydata/xarray/issues/7358
         # NaN values should remain at the end when sorting in descending order