import_metadata==5.0.0 causes error when loading netcdf file

[EtienneCmb]

What happened?

Loading an .nc file under Python 3.7 and with the latest importlib_metadata==5.0.0 doesn't work.

What did you expect to happen?

File should be loaded.

Minimal Complete Verifiable Example

# Python version 3.7
# import_metadata==5.0.0

import xarray as xr
import numpy as np

data = xr.DataArray(
    np.random.rand(10, 20)
)
data.to_netcdf('test.nc')
xr.load_dataarray('test.nc')

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.

Relevant log output

Traceback (most recent call last):
  File "xarray_bug.py", line 7, in <module>
    xr.load_dataarray('test.nc')
  File "/home/etienne/anaconda3/envs/py37/lib/python3.7/site-packages/xarray/backends/api.py", line 267, in load_dataarray
    with open_dataarray(filename_or_obj, **kwargs) as da:
  File "/home/etienne/anaconda3/envs/py37/lib/python3.7/site-packages/xarray/backends/api.py", line 666, in open_dataarray
    **kwargs,
  File "/home/etienne/anaconda3/envs/py37/lib/python3.7/site-packages/xarray/backends/api.py", line 479, in open_dataset
    engine = plugins.guess_engine(filename_or_obj)
  File "/home/etienne/anaconda3/envs/py37/lib/python3.7/site-packages/xarray/backends/plugins.py", line 110, in guess_engine
    engines = list_engines()
  File "/home/etienne/anaconda3/envs/py37/lib/python3.7/site-packages/xarray/backends/plugins.py", line 105, in list_engines
    entrypoints = entry_points().get("xarray.backends", ())
AttributeError: 'EntryPoints' object has no attribute 'get'

Anything else we need to know?

• Only with importlib_metadata==5.0.0
• Doesn't works with Python 3.7 but it works with 3.9
• Similar problem for flake8 repo.
• They solved it by imposing a specific version for python versions under 3.8 : https://github.com/PyCQA/flake8/blob/2c1bfa1f3d85e4d94ebc3b6d601d454a09d8043e/setup.cfg#L44

Environment

INSTALLED VERSIONS

commit: None
python: 3.7.12 | packaged by conda-forge | (default, Oct 26 2021, 06:08:21)
[GCC 9.4.0]
python-bits: 64
OS: Linux
OS-release: 5.4.210-1-MANJARO
machine: x86_64
processor:
byteorder: little
LC_ALL: None
LANG: fr_FR.UTF-8
LOCALE: ('fr_FR', 'UTF-8')
libhdf5: 1.12.2
libnetcdf: 4.9.0

xarray: 0.20.2
pandas: 1.3.5
numpy: 1.21.6
scipy: None
netCDF4: 1.6.1
pydap: None
h5netcdf: 1.0.2
h5py: 3.7.0
Nio: None
zarr: None
cftime: 1.6.2
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
fsspec: None
cupy: None
pint: None
sparse: None
setuptools: 65.4.1
pip: 22.2.2
conda: None
pytest: None
IPython: 7.34.0
sphinx: None

[Illviljan]

Hello,

We try to follow nep-29 and intend to only support python >=3.8:

xarray/setup.cfg

Lines 72 to 76 in f5884a2

	[options]
	packages = find:
	zip_safe = False # https://mypy.readthedocs.io/en/latest/installed_packages.html
	include_package_data = True
	python_requires = >=3.8

There's a change to this behavior in 3.10 as well, see:

xarray/xarray/backends/plugins.py

Lines 101 to 105 in f5884a2

	# New selection mechanism introduced with Python 3.10. See GH6514.
	if sys.version_info >= (3, 10):
	entrypoints = entry_points(group="xarray.backends")
	else:
	entrypoints = entry_points().get("xarray.backends", ())

[EtienneCmb]

Ok, thank you. I need to update my env then :)

[Illviljan]

If you want to investigate more, feel free to try with python 3.8 as well.
Our CI seems to install importlib-metadata 4.11.4 py310hff52083_0 conda-forge for python 3.8 so maybe there's an issue there?

[dcherian]

I need to update my env then

Thanks @EtienneCmb

[observingClouds]

I was about to open the same issue but can confirm that I only get an issue with python<3.8 and importlib_metadata==5.0.0
@Illviljan , importlib-metadata should not be necessary for python>=3.8 as it became part of the standard library.