issues: 856900805

While working on a pull request (#5149) for #5146 I came across an inconsistency in allowed dimension names. If I try and create a DataArray with a non-string dimension, I get a TypeError:

```python console

import xarray as xr da = xr.DataArray(np.ones((5, 5)), dims=[1, "y"]) ... TypeError: dimension 1 is not a string ```

But creating it with a string and renaming it works:

```python console

da = xr.DataArray(np.ones((5, 5)), dims=["x", "y"]).rename(x=1) da <xarray.DataArray (1: 5, y: 5)> array([[1., 1., 1., 1., 1.], [1., 1., 1., 1., 1.], [1., 1., 1., 1., 1.], [1., 1., 1., 1., 1.], [1., 1., 1., 1., 1.]]) Dimensions without coordinates: 1, y ```

I can create a dataset via this renaming, but trying to get the repr value fails as xarray.core.utils.SortedKeysDict tries to sort it and cannot compare the string dimension to the int dimension:

```python console

import xarray as xr ds = xr.Dataset({"test": xr.DataArray(np.ones((5, 5)), dims=["x", "y"]).rename(x=1)}) ds ... ~/software/external/xarray/xarray/core/formatting.py in dataset_repr(ds) 519 520 dims_start = pretty_print("Dimensions:", col_width) --> 521 summary.append("{}({})".format(dims_start, dim_summary(ds))) 522 523 if ds.coords:

~/software/external/xarray/xarray/core/formatting.py in dim_summary(obj) 422 423 def dim_summary(obj): --> 424 elements = [f"{k}: {v}" for k, v in obj.sizes.items()] 425 return ", ".join(elements) 426

~/software/external/xarray/xarray/core/formatting.py in <listcomp>(.0) 422 423 def dim_summary(obj): --> 424 elements = [f"{k}: {v}" for k, v in obj.sizes.items()] 425 return ", ".join(elements) 426

/usr/lib/python3.9/_collections_abc.py in iter(self) 847 848 def iter(self): --> 849 for key in self._mapping: 850 yield (key, self._mapping[key]) 851

~/software/external/xarray/xarray/core/utils.py in iter(self) 437 438 def iter(self) -> Iterator[K]: --> 439 return iter(self.mapping) 440 441 def len(self) -> int:

~/software/external/xarray/xarray/core/utils.py in iter(self) 504 def iter(self) -> Iterator[K]: 505 # see #4571 for the reason of the type ignore --> 506 return iter(sorted(self.mapping)) # type: ignore[type-var] 507 508 def len(self) -> int:

TypeError: '<' not supported between instances of 'str' and 'int' ``` The same thing happens if I call rename on the dataset rather than the array it is initialised with.

If the initialiser requires the dimension names to be strings, and other code (which includes the HTML formatter I was looking at when I found this) assume that they are, then rename and any other method which can alter dimension names should also enforce the string requirement.

Environment:

Output of <tt>xr.show_versions()</tt>

INSTALLED VERSIONS ------------------ commit: 851d85b9203b49039237b447b3707b270d613db5 python: 3.9.2 (default, Feb 20 2021, 18:40:11) [GCC 10.2.0] python-bits: 64 OS: Linux OS-release: 5.11.13-arch1-1 machine: x86_64 processor: byteorder: little LC_ALL: None LANG: en_NZ.UTF-8 LOCALE: en_NZ.UTF-8 libhdf5: 1.12.0 libnetcdf: 4.7.4 xarray: 0.17.0 pandas: 1.2.3 numpy: 1.20.1 scipy: 1.6.2 netCDF4: 1.5.6 pydap: None h5netcdf: 0.10.0 h5py: 3.2.1 Nio: None zarr: None cftime: 1.4.1 nc_time_axis: None PseudoNetCDF: None rasterio: 1.2.2 cfgrib: None iris: None bottleneck: 1.3.2 dask: 2021.03.0 distributed: 2021.03.0 matplotlib: 3.4.1 cartopy: 0.18.0 seaborn: 0.11.1 numbagg: None pint: None setuptools: 54.2.0 pip: 20.3.1 conda: None pytest: 6.2.3 IPython: 7.22.0 sphinx: 3.5.4