How to use a local flake8 plugin with a python virtual env?

Question

I'm trying to integrate a project with a flake8 plugin I wrote as a local plugin (not a PyPI package for example) as explained here. The project uses a virtual env, both locally and as a github workflow. Since flake8 is invoked from within the virtual env it can't find the plugin, which resides as a folder under the project root. When I manually add the plugin code to the virtual env folder it integrates nicely and flake8 is able to find to execute it.

The solution smells like some kind of github pre-commit-config/hook, but I can't find any reference in the docs for this usecase. Currently flake8 is configured in pre-commit-config like so:

  repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.2.0
    hooks:
      - id: debug-statements
  - repo: https://github.com/PyCQA/flake8
    rev: 4.0.1
    hooks:
      - id: flake8
        additional_dependencies: ['dlint']

Is there a way to use my non-packaged flake8 plugin with a virtual env locally / in a github workflow?

Answer 1

you'll want to configure paths to make sure that flake8 puts the appropriate directories on sys.path to discover your plugin

this is mentioned in the docs you linked, just a little bit further down:

However, if you are working on a project that isn’t set up as an installable package, or Flake8 doesn’t run from the same virtualenv your code runs in, you may need to tell Flake8 where to import your local plugins from. You can do this via the paths option in the local-plugins section of your config:

[flake8:local-plugins]
extension =
  MC1 = myflake8plugin:MyChecker1
paths =
  ./path/to

note that if your local plugin has dependencies it needs, those will also be needed to be listed in additional_dependencies in your pre-commit configuration

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disclaimer: I'm the current flake8 maintainer, and I created pre-commit