Fail to sel() when index comes from categorical pandas Series

[mancellin]

Dear xarray team,

Thank you very much for your work on this useful package.
Here is a bug I just found in my code.

MCVE Code Sample

Creating a Dataset from pandas when the coordinate is a categorical series:

import pandas as pd

ind = pd.Series(['foo', 'bar'], dtype='category')
df = pd.DataFrame({'ind': ind, 'values': [1, 2]})
df = df.set_index('ind')

ds = df.to_xarray()

print(ds.sel(ind='foo'))

Expected Output

When ind is not categorical, the code returns the expected output:

<xarray.Dataset>
Dimensions:  ()
Coordinates:
    ind      <U3 'foo'
Data variables:
    values   int64 1

Problem Description

When ind is categorical, it fails and gives the following traceback:

Traceback (most recent call last):
  File "/home/matthieu/foo.py", line 9, in <module>
    print(ds.sel(ind='foo'))
  File "/opt/anaconda3/envs/issue/lib/python3.8/site-packages/xarray/core/dataset.py", line 2013,
in sel
    pos_indexers, new_indexes = remap_label_indexers(
  File "/opt/anaconda3/envs/issue/lib/python3.8/site-packages/xarray/core/coordinates.py", line 39
1, in remap_label_indexers
    pos_indexers, new_indexes = indexing.remap_label_indexers(
  File "/opt/anaconda3/envs/issue/lib/python3.8/site-packages/xarray/core/indexing.py", line 260,
in remap_label_indexers
    idxr, new_idx = convert_label_indexer(index, label, dim, method, tolerance)
  File "/opt/anaconda3/envs/issue/lib/python3.8/site-packages/xarray/core/indexing.py", line 179,
in convert_label_indexer
    indexer = index.get_loc(
TypeError: get_loc() got an unexpected keyword argument 'tolerance'

Output of xr.show_versions()

commit: None python: 3.8.0 (default, Nov 6 2019, 21:49:08) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 4.19.91-1-MANJARO machine: x86_64 processor: byteorder: little LC_ALL: None LANG: fr_FR.UTF-8 LOCALE: fr_FR.UTF-8 libhdf5: None libnetcdf: None

xarray: 0.14.1
pandas: 0.25.3
numpy: 1.17.4
scipy: None
netCDF4: None
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: None
cartopy: None
seaborn: None
numbagg: None
setuptools: 44.0.0.post20200106
pip: 19.3.1
conda: None
pytest: None
IPython: None
sphinx: None

[fujiisoup]

Thanks, @mancellin

I sent a quick fix.
Please feel free to comment there.

[mancellin]

Your patch fixes the issue, thank you!

FYI, found another issue with categorical values: #3674

[fujiisoup]

Let's close this after #3670 is merged.