Python 3.7 compatibility issue introduced by release 1.3.0

[nicolas-seichepine]

Hi,

If I understand correctly, latest release should work with python 3.7

In the meantime, this specific line introduced in release 1.3.0 breaks compatibility (ImportError: cannot import name '_MAX_WINDOWS_WORKERS' from 'concurrent.futures.process')

[imatiach-msft]

I'm seeing a similar error on windows python 3.7:

File "C:\Miniconda\envs\test\lib\site-packages\joblib\externals\loky\backend\popen_loky_win32.py", line 153, in main
_winapi.SYNCHRONIZE | _winapi.PROCESS_DUP_HANDLE, False, parent_pid
AttributeError: module '_winapi' has no attribute 'SYNCHRONIZE'

trying to pin joblib < 1.3.0 in the tests for now...

[glutamatt]

some hints :

[1C4nfaN]

the version cpython<=3.7.3 does not define _MAX_WINDOWS_WORKERS

[tomMoral]

Thanks a lot for the report and investigations.
I opened a PR to fix this in loky (joblib/loky#408). I will try to do a bug fix release asap, feel free to let us know if anything else come up before this.

[imatiach-msft]

Seems my problem is a bit different, I created a new issue here:

joblib/loky#411

[tomMoral]

The problem should be resolved on unix platform with the release 1.3.1.
Let us know if more problem persists.

For windows user, a potential way around is to use the spawn processes in `loky, which should provide a relatively good support but might still have some issues with controlling the C-level parallelism for instance with numpy.

from joblib.externals.loky.backend.context import set_start_method

set_start_method('spawn')

[imatiach-msft]

I just pinned to joblib<1.3.0 on python 3.7 & windows platform and it works for now. I think most of our users are on unix anyway and python 3.8 or greater but we like to exhaustively test every python/platform/oss package combination.