More informative error for passing a list to dataset.transpose

doc/whats-new.rst

@@ -33,7 +33,8 @@ Deprecations
 
 Bug fixes
 ~~~~~~~~~
-
+- Fixed :py:meth:`Dataset.transpose` to raise a more informative error. (:issue:`6502`, :pull:`7120`)
+  By `Patrick Naylor <https://github.com/patrick-naylor>`_
 
 Documentation
 ~~~~~~~~~~~~~

xarray/core/dataset.py

@@ -5401,6 +5401,13 @@ def transpose(
         numpy.transpose
         DataArray.transpose
         """
+        # Raise error if list is passed as dims
+        if (len(dims) > 0) and (isinstance(dims[0], list)):
+            list_fix = [f"'{x}', " if isinstance(x, str) else f"{x}, " for x in dims[0]]
+            raise TypeError(
+                f'transpose requires dims to be of hashable type. Expected "{"".join(list_fix)[:-2]}". Received "{dims[0]}" instead'
+            )
+
         # Use infix_dims to check once for missing dimensions
         if len(dims) != 0:
             _ = list(infix_dims(dims, self.dims, missing_dims))

xarray/tests/test_dataset.py

@@ -6806,3 +6806,14 @@ def test_string_keys_typing() -> None:
     ds = xr.Dataset(dict(x=da))
     mapping = {"y": da}
     ds.assign(variables=mapping)
+
+
+def test_traspose_error() -> None:
+    # Transpose dataset with list as argument
+    # Should raise error
+    ds = xr.Dataset({"foo": (("x", "y"), [[21]]), "bar": (("x", "y"), [[12]])})
+
+    with pytest.raises(
+        TypeError, match=r"transpose requires dims to be of hashable type.*"
+    ):
+        ds.transpose(["y", "x"])