NameError: name '_DType_co' is not defined

[monocongo]

What happened: I installed a package that has xarray as a dependency. I then ran the package's console script, which resulted in the NameError shown below.

What you expected to happen: Successful import of the xarray package.

Minimal Complete Verifiable Example:

$ conda create -n tstenv python=3.7
$ conda activate tstenv
(tstenv) $ pip install climate-indices
(tstenv) $ python
>>> import xarray
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/james/miniconda3/envs/tstenv/lib/python3.7/site-packages/xarray/__init__.py", line 3, in <module>
    from . import testing, tutorial, ufuncs
  File "/home/james/miniconda3/envs/tstenv/lib/python3.7/site-packages/xarray/testing.py", line 8, in <module>
    from xarray.core import duck_array_ops, formatting, utils
  File "/home/james/miniconda3/envs/tstenv/lib/python3.7/site-packages/xarray/core/duck_array_ops.py", line 16, in <module>
    from . import dask_array_compat, dask_array_ops, dtypes, npcompat, nputils
  File "/home/james/miniconda3/envs/tstenv/lib/python3.7/site-packages/xarray/core/npcompat.py", line 81, in <module>
    from numpy.typing import ArrayLike, DTypeLike
  File "/home/james/miniconda3/envs/tstenv/lib/python3.7/site-packages/numpy/typing/__init__.py", line 316, in <module>
    from ._dtype_like import (
  File "/home/james/miniconda3/envs/tstenv/lib/python3.7/site-packages/numpy/typing/_dtype_like.py", line 95, in <module>
    class _SupportsDType(Generic[_DType_co]):

Anything else we need to know?:
This does not happen if I just install xarray, so there seems to be a conflict with another dependency package at play here. Are there methods for finding namespace conflicts like this without resorting to a "manual" method of trying all the various combinations? It seems that I've included a version of another package in my requirements that has a namespace conflict with xarray -- how can I work out which this is? Or maybe a simpler solution is to not use specific versions in the requirements.txt of the package and instead let conda work out the correct/latest versions?

Thanks in advance for any ideas on where to look to resolve this issue (and in general for all the work that goes into xarray's care and feeding).

Environment:
Linux (Ubuntu 20.04)
Anaconda, Python 3.7

$ conda list xarray
# packages in environment at /home/james/miniconda3/envs/tstenv:
#
# Name                    Version                   Build  Channel
xarray                    0.18.2                   pypi_0    pypi

[max-sixty]

@monocongo does it raise an error if you try importing numpy without xarray installed?

[menzel-gfdl]

I get the same error, but can import numpy with/without xarray installed. I'm running python 3.7.7 on RHEL 7.9 (Maipo):

$ pip install --upgrade pip
$ pip install xarray
$ python3
>>> import numpy
>>> import xarray
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "env/lib/python3.7/site-packages/xarray/__init__.py", line 3, in <module>
    from . import testing, tutorial, ufuncs
  File "env/lib/python3.7/site-packages/xarray/testing.py", line 8, in <module>
    from xarray.core import duck_array_ops, formatting, utils
  File "env/lib/python3.7/site-packages/xarray/core/duck_array_ops.py", line 16, in <module>
    from . import dask_array_compat, dask_array_ops, dtypes, npcompat, nputils
  File "env/lib/python3.7/site-packages/xarray/core/npcompat.py", line 81, in <module>
    from numpy.typing import ArrayLike, DTypeLike
  File "env/lib/python3.7/site-packages/numpy/typing/__init__.py", line 316, in <module>
    from ._dtype_like import (
  File "env/lib/python3.7/site-packages/numpy/typing/_dtype_like.py", line 95, in <module>
    class _SupportsDType(Generic[_DType_co]):
NameError: name '_DType_co' is not defined

[shoyer]

What happens if you just write import numpy.typing ?

[menzel-gfdl]

I get the same error, as expected:

>>> import numpy.typing
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "env/lib/python3.7/site-packages/numpy/typing/__init__.py", line 316, in <module>
    from ._dtype_like import (
  File "env/lib/python3.7/site-packages/numpy/typing/_dtype_like.py", line 95, in <module>
    class _SupportsDType(Generic[_DType_co]):
NameError: name '_DType_co' is not defined
>>> numpy.version.version
'1.21.1'

numpy is aware of this issue. It looks like it is only an issue for python 3.7.

[shoyer]

OK, closing this over here since it seems to be a bug with numpy rather than xarray

[rhkleijn]

From numpy/numpy#19521: installing typing-extensions may help when running on python 3.7.

[monocongo]

Thanks to all for your help. Installing typing-extensions did solve the problem, thanks for the heads up @rhkleijn