More informative error for passing a list to dataset.transpose (#7120)

* Added statement to check if list is passed for dims and raise a more helpful error

* Fixed issue where isinstance would not work when no arguments are passed

* Added test

* Updated whats-new.rst

* Updated whats-new.rst with pull number

* Removed test print statement

* Update xarray/core/dataset.py

Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>

* Fixed test to inclued whole error output and imported regex. Changed transpose join statement

* Hopefully fixed typecheck error and improved readability from suggestions by @max-sixty

Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>

Author: patrick-naylor

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"{repr(x)}" if isinstance(x, str) else f"{x}" for x in dims[0]]
+            raise TypeError(
+                f'transpose requires dims to be passed as multiple arguments. Expected `{", ".join(list_fix)}`. 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

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import pickle
+import re
 import sys
 import warnings
 from copy import copy, deepcopy
@@ -6806,3 +6807,17 @@ def test_string_keys_typing() -> None:
     ds = xr.Dataset(dict(x=da))
     mapping = {"y": da}
     ds.assign(variables=mapping)
+
+
+def test_transpose_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=re.escape(
+            "transpose requires dims to be passed as multiple arguments. Expected `'y', 'x'`. Received `['y', 'x']` instead"
+        ),
+    ):
+        ds.transpose(["y", "x"])  # type: ignore