pip install fails with python 3.8

[o-smirnov]

@gijzelaerr @Athanaseus advice needed. I can't understand if this is an Oleg brain bug or a pip bug, or just normal life.

My current dev branch (and master, for all I know) fails to pip install -e. The error occurs when installing https://github.com/ratt-ru/radiopadre/blob/b1.2.x/requirements.txt:

Exception: Error retrieving astropy-helpers from PyPI:
ContextualVersionConflict(pyparsing 3.0.6 (/users/oms/.radiopadre/venv/lib/python3.8/site-packages), Requirement.parse('pyparsing<3,>=2.0.2'), {'packaging'})

I can work around it by adding pyparsing<3 to the requirements. But I don't understand why I need to be doing this ritual dance. As far as I can tell:

• I don't need pyparsing and I'd really rather not know what it is!

• one of my dependency packages (call it X) requires pyparsing, which is at version 3.0.6 currently, this is cheerfully pulled in

• another dependency package (call it Y) requires packaging, which is also pulled in, but it has a specific pyparsing<3 dependency. So it says sorry, I can't deal with this shit

• if I explicitly add pyparsing<3 to my dependencies, both X and Y are happy.

But why do I need to worry about the specific version of a dependency of a dependency? Shouldn't pip be able to work out this solution automatically? Or am I doing something wrong here?

[Mulan-94]

@o-smirnov I've met this issue with ragavi my resort has been using pip with --use-deprecated=legacy-resolver but this:
https://pip.pypa.io/en/latest/user_guide/#changes-to-the-pip-dependency-resolver-in-20-3-2020 can shed more light

[o-smirnov]

Thanks @Mulan-94, that put me on the right track... but actually, turns out pip install -U pip setuptools is the answer, which I really ought to have known by now! So it's "Oleg brain bug" I guess...

[gijzelaerr]

wanted to say the same thing as @Mulan-94 , recent pip comes with a stricter dep solver, which breaks things that worked before. Maybe the latest latest pip has an even better dep solver that solves your issue.