Pants Format and Lint Check

When to Use

Apply this skill automatically when:

• Finishing implementation of a feature or fix
• User asks to format, lint, or check code
• Before committing changes
• After modifying Python files

Workflow

Follow these steps in order:

Step 1: Remove Unused Imports

Remove unused imports first to prevent common linting errors:

pants --changed-since=HEAD fix ::

This fixes import issues automatically before running full checks.

Step 2: Run Full Format, Lint, and Check

Run the complete pants check suite:

pants fmt lint check ::

This command:

• fmt: Auto-formats code (isort, black, etc.)
• lint: Runs linters (flake8, pylint, etc.)
• check: Runs type checking (mypy)

Step 3: Review and Fix Remaining Issues

If errors remain after Step 2:

1. Read the error output - pants provides specific file locations and line numbers
2. Fix the issues - address each error reported
3. Re-run: pants fmt lint check ::
4. Repeat until all checks pass

Common Issues and Solutions

Import Errors

If you see "unused import" or "import not found":

• Remove unused imports
• Add missing dependencies to BUILD files
• Check import paths are correct

Type Errors

If mypy reports type issues:

• Add type hints where missing
• Fix incorrect type annotations
• Use # type: ignore comments only as a last resort

Style Errors

If flake8/pylint reports style issues:

• Most are auto-fixed by pants fmt
• For manual fixes, follow the error message guidance
• Check .flake8 and .isort.cfg for project conventions

Success Criteria

✅ All checks pass with no errors ✅ No warnings that need attention ✅ Code is properly formatted and typed

Notes

• Run this from the repository root (where pants.toml is located)
• The :: selector checks all targets in the repo
• For faster checks on specific files, use: pants fmt lint check path/to/file.py
• Always run before creating commits to catch issues early