Pylint "Unable to import <module>" error

[memeLordo]

I've searched open issues for similar requests

• [X] Yes

I've manually reviewed logs to find potential errors

• [X] Yes

I've recently downloaded the latest plugin version of mason.nvim

• [X] Yes

Problem description

It's not a critical issue, but an annoying one. Basically, I have an import error of my Python code for my Pylint module. And for some cases it solvable by just writing a path to .pylintrc or using nul-ls package. But whatever I try, the problem can’t be solved by me or I just ran out of ideas.

Expected behavior

No "Unable to import " error as with other linters (like Pylama, Flake8 and so on) Same code with Flake8

Steps to reproduce

1. Install the module via Mason on latest Astrovim configuration.
2. Create a Python file using neovim (ex. nvim main.py)
3. Import any non-base Python library, installed with pip
4. Get an error.

Affected packages

Pylint, mypy (getting the same error)

Neovim version (>= 0.7)

NVIM v0.8.3 Build type: Release LuaJIT 2.1.0-beta3

Operating system/version

Ubuntu 22.04.2 LTS

Healthcheck

ERROR: No healthcheck found for "mason" plugin.

Screenshots or recordings

[williamboman]

Hello! So pip packages (which pylint is) will be installed to a separate virtual environment by Mason. pylint will by default only look for packages inside that virtual environment, which is a bit problematic.

It seems like you have three options (either first two if you want to use pylint via Mason): 1) Set the $PYTHONPATH environment variable to point to the location you have your dependencies installed, for example:

$ export PYTHONPATH="$PWD/.venv/lib/python3.8/site-packages"
$ nvim

Note that you only need to set this PYTHONPATH variable for the pylint process itself, if you use null-ls you can instead do something like:

    null_ls.builtins.diagnostics.pylint.with({
        env = function(params)
            return { PYTHONPATH = vim.fn.expand(params.root .. "/.venv/lib/*/site-packages") }
        end,
    }),

2) Use the --init-hook configuration in pylint:

# .pylintrc
[MASTER]
init-hook='import sys; import os; sys.path.append(os.path.join(os.getcwd(), ".venv", "lib", "python3.8", "site-packages"))'

3) Install pylint in the same environment where your dependencies exist, likely in a project-local virtual environment. In this case you'll want to uninstall pylint from Mason.

[williamboman]

The same can be achieved for mypy but through a different command flag, --python-executable (should be configurable in null-ls via extra_args, similar to pylint example above).

[dbatten5]

I'm having a similar issue whereby I have a mypy installed via Mason (as I want to have it for all projects on my laptop) and in a virtual environment for a currently active work project (since it's part of the dependencies for the project). If I run :!which mypy, it points to the mason installation as the mason bin folder appears ahead of the /Users/{my_username"/.virtualenvs/{work_project}/bin folder. Specifying the --python-executable arg isn't ideal as I would have to specify the {work_project} name in the path which would then break for other projects using mypy. Is there any way to ensure that virtual envs appear ahead of mason in my $PATH? Ideally I'd have a way for mason to append to $PATH, not prepend.

EDIT: just found there's a config option to do exactly that. Should have read the docs 🤦