DataTree constructor error message says dict even though dict is not accepted

[mgunyho]

What happened?

When I try to create a DataTree with a dict as the first argument, I get a TypeError:

>>> xr.DataTree(dict())
...
TypeError: data object is not an xarray.Dataset, dict, or None: {}

What did you expect to happen?

A dictionary should be accepted, or the error message should not say that the argument could be a dict.

I suppose this is a leftover from some earlier iteration of the API?

Minimal Complete Verifiable Example

# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "xarray[complete]@git+https://github.com/pydata/xarray.git@main",
# ]
# ///
#
# This script automatically imports the development branch of xarray to check for issues.
# Please delete this header if you have _not_ tested this script with `uv run`!

import xarray as xr
xr.show_versions()
# your reproducer code ...

xr.DataTree(dict())

Steps to reproduce

No response

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

File .../xarray/xarray/core/datatree.py:547, in DataTree.__init__(self, dataset, children, name)
    517 def __init__(
    518     self,
    519     dataset: Dataset | Coordinates | None = None,
    520     children: Mapping[str, DataTree] | None = None,
    521     name: str | None = None,
    522 ):
    523     """
    524     Create a single node of a DataTree.
    525 
   (...)    545     DataTree.from_dict
    546     """
--> 547     self._set_node_data(_to_new_dataset(dataset))
    549     # comes after setting node data as this will check for clashes between child names and existing variable names
    550     super().__init__(name=name, children=children)

File .../xarray/xarray/core/datatree.py:143, in _to_new_dataset(data)
    141     ds = Dataset()
    142 else:
--> 143     raise TypeError(f"data object is not an xarray.Dataset, dict, or None: {data}")
    144 return ds

Anything else we need to know?

No response

Environment

Details

INSTALLED VERSIONS

commit: 80b6a92
python: 3.13.5 (main, Jun 12 2025, 12:40:22) [Clang 20.1.4 ]
python-bits: 64
OS: Linux
OS-release: 7.1.4-204.fc44.x86_64
machine: x86_64
processor:
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.14.6
libnetcdf: 4.9.3

xarray: 2026.7.1.dev24+g80b6a9260.d20260806
pandas: 3.0.5
numpy: 2.4.6
scipy: 1.18.0
netCDF4: 1.7.4
pydap: 3.5.10
h5netcdf: 1.8.1
h5py: 3.16.0
zarr: 3.3.0
cftime: 1.6.5
nc_time_axis: 1.4.1
iris: None
bottleneck: 1.6.0
dask: 2026.7.1
distributed: 2026.7.1
matplotlib: 3.11.1
cartopy: 0.25.0
seaborn: 0.13.2
numbagg: 0.9.4
fsspec: 2026.7.0
cupy: None
pint: None
sparse: 0.19.1
flox: 0.11.2
numpy_groupies: 0.11.3
setuptools: None
pip: None
conda: None
pytest: 9.1.1
mypy: 1.19.1
IPython: 9.16.1
sphinx: 8.2.3