Understanding pre-commit Configuration: Why exclude Doesn't Work with mypy

Dive into the nuances of using `pre-commit`'s `exclude` configuration with `mypy`. Understand why `mypy` still checks certain files and how to effectively manage imports.
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Understanding pre-commit Configuration: Why exclude Doesn't Work with mypy

The Problem

You may have a configuration file, like below, aiming to exclude a directory from checks:

[[See Video to Reveal this Text or Code Snippet]]

Despite setting the exclude, you still see errors from files in the excluded src/project/proto/ directory when running mypy. So, what’s going wrong?

The Explanation

Dynamic Analysis with mypy

mypy operates differently than some other hooks. It performs dynamic analysis and may follow imports that exist in the files you face during your workflow. This means:

Even with an exclude configuration in pre-commit, mypy doesn’t just limit itself to the specified paths.

If there are imports in files that mypy checks, it will analyze those paths as well, even if they lead to excluded directories.

The Role of follow-imports

The behavior you’re experiencing is largely impacted by the follow-imports setting in mypy.

By default, mypy tracks imports, which can lead it to check files from your excluded directories.

The Solution

To resolve this issue, you should configure mypy to ignore errors from the specific directories or files you wish to exclude. Here are the steps you can take:

[[See Video to Reveal this Text or Code Snippet]]

This tells mypy to ignore missing imports for all files in the specified directory.

Step 2: Use the --follow-imports Flag

If needed, adjust the follow_imports behavior directly in the mypy command arguments:

[[See Video to Reveal this Text or Code Snippet]]

This will ensure that mypy does not follow imports from your excluded files, helping minimize unwanted error messages.

Conclusion

By understanding how mypy interacts with your pre-commit configuration, you can take effective steps to manage analyses and focus on relevant errors. Remember, the exclude directive does not limit mypy behaviors inherently because of how it handles imports and analyses directories. Adjusting .ini configurations and mypy flags will offer you greater control over which files are included and which are ignored during checks.

Remember:

Review your mypy settings frequently to make sure they align with the structure of your project.

Continuously experiment with the exclusion rules and mypy flags to tailor your workflow optimally.

By applying these guidelines, you’ll maintain a clean and efficient codebase without unnecessary distractions from ignored errors!