See also #5236 which could be related which uses conda.

I tried to scour through pip and pytest issues, but I can't find a discussion on this. pip and pytest and pycacheare too generic keywords. I even found pytest plugin to remove bytecode but it does not work ~~anymore~~ for me.

I proposed a fix in #6039, which I believe is good to have, as you can't expect every user to execute with python -B or set PYTHONDONTWRITEBYTECODE while running tests.

I don't think xarray has anything to do with that issue: if python -c 'import dask' succeeds, xarray will have to assume dask is available.

You will probably have to investigate pip (why didn't it remove the __pycache__ directory?) or pytest (why was the pyc file created in the first place?) to really fix this, but for now you can try setting PYTHONDONTWRITEBYTECODE or running python with -B (for example, python -B -m pytest)

This in my opinion is a cascade of multiple issues: - pytest creates special bytecode - pip does not clean the whole __pycache__ directory on uninstall - xarray.pycompat.is_duck_dask_array uses importlib.import_module('dask') to determine if it is installed.

@twhughes @keewis In my case, I encounter this when I: - Have xarray + dask installed in my environment - Run any pytest which imports xarray (which in turn imports dask) - Uninstall dask, but pytest artefacts remain:

sh ❯ ls venv/lib/python3.9/site-packages/dask/__pycache__ utils_test.cpython-39-pytest-6.2.5.pyc

Here are the steps which would hopefully reproduce the behaviour:

```py

Create this small unit test named:

test_import_xarray.py

def test_xr(): import xarray ```

```sh python -m venv venv source venv/bin/activate pip install xarray pytest dask pytest test_import_xarray.py

pip uninstall dask ls venv/lib/python3.9/site-packages/dask/pycache # See output above python -c 'import dask' # No ImportError! python -c 'import xarray' ```

Exact versions used Python 3.9.9 along with: ```sh

requirements.txt

attrs==21.2.0 cloudpickle==2.0.0 dask==2021.11.2 fsspec==2021.11.1 iniconfig==1.1.1 locket==0.2.1 numpy==1.21.4 packaging==21.3 pandas==1.3.4 partd==1.2.0 pluggy==1.0.0 py==1.11.0 pyparsing==3.0.6 pytest==6.2.5 python-dateutil==2.8.2 pytz==2021.3 PyYAML==6.0 six==1.16.0 toml==0.10.2 toolz==0.11.2 xarray==0.20.1 ```

Hm, ok this seems to pass for me as well. I will have to look into it a bit more, thanks for your advice.

On Sun, Oct 17, 2021 at 9:50 AM keewis @.***> wrote:

I still can't reproduce if I create the environment using

python3.9 -m venv testsource test/bin/activate python -m pip install xarray python -c 'import xarray'

Looking at the traceback you posted it seems you've been trying to install into /usr/local/lib/python3.9? That's something you should avoid as much as possible, unless you're trying to build OS packages.

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I still can't reproduce if I create the environment using sh python3.9 -m venv test source test/bin/activate python -m pip install xarray python -c 'import xarray'

Looking at the traceback you posted it seems you've been trying to install into /usr/local? That's something you should avoid as much as possible (unless you're trying to build OS packages).

Thanks. Note I am using venv(not conda) on python 3.9.
So after creation of a clean environment and then pip install xarray I needed pip install dask to not see this error.

closing as a environment issue, but feel free to ask if you need more help

I don't think there is, unfortunately

Actually It doesn't seem to be so simple, I will try to isolate the issue n my installation. Is there any way to disable dask explicitly so I can bypass this error?

Appreciate the help @keewis, I did some investigative work and it seems to work fine until I install PyYAML.

that's strange, we even have a CI to make sure importing without having dask installed works. I also can't reproduce with bash mamba create -n test python=3.9.7 # new clean environment python -m pip install xarray python -c 'import xarray as xr' so maybe there's something wrong with your environment?