[Question] why can't we add pylint in this repo hooks.yaml file?

[lavish205]

My .pre-commit-config.yaml file looks like this:

-   repo: https://github.com/pre-commit/pre-commit-hooks
     sha: 52582865ab7ed8f41734253190844c854ddd9a9e
     hooks:
     -   id: trailing-whitespace
     -   id: check-ast
     -   id: debug-statements
     -   id: end-of-file-fixer
-   repo: git://github.com/pre-commit/mirrors-pylint
     sha: v1.6.4
     hooks:
    -   id: pylint

and when I run pre-commit install it creates a repo for pylint in ~/.pre-commit/repoXXXX/ with its own virtual env in it, due to which pylint shows import errors.
So there are two ways to solve this error:

1. add all required packages in additional_dependencies in .pre-commit-config.yaml file for pylint.
   But I can't add all the packages here because it useless to create two virtual env with same packages.
   Can we however, merge it with our own virtualenv??

2. if I modify pre-commit-hooks/hooks.yaml and add pylint hook over there, it works perfectly fine.

Can you suggest me which is the best way to do it??

[asottile]

So tl;dr is pylint does some static analysis and some dynamic analysis. When put in an isolated virtualenv it does not work properly. Using isolated virtualenvs achieves the design goal of reproducibility in pre-commit.

That said, there are still a few options for using pylint with pre-commit:

• disable the dynamic checking parts (not usually the desirable option)
• use it as a "system" hook (usually through "local" hooks).

You can find some related issues:

• Allow using system wide python modules pre-commit#362
• Unable to determine how to use pre-existing virtualenv for a hook pre-commit#266
• pre-commit doesn't keep current project/virtualenv in sys.path pre-commit#178
• https://github.com/Yelp/venv-update/blob/de9e1befdecf448cf02ceb5c57a30bcc88a58c06/.pre-commit-config.yaml#L30-L36
• http://pre-commit.com/#repository-local-hooks