Configuration Files

Linters read config from files in priority order:

1. CLI flags (--max-line-length=120).
2. pyproject.toml [tool.linter] section (modern).
3. Legacy .flake8, .pylintrc files.
4. Defaults.

Config controls:

• Enabled rules: enable = [E501, W292] or disable = [...].
• Severity per rule: error / warning / info.
• Per-rule options: max-line-length=100, max-complexity=15.
• Per-file overrides: [per-file-ignores] tests/*.py = E501.

Example pyproject.toml:

[tool.ruff]
line-length = 100
select = ["E", "F", "W", "B"]
ignore = ["E501"]

[tool.ruff.per-file-ignores]
"tests/**" = ["S101"]   # allow assert in tests

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Inheritance: nested directories can have own config files (extend = "../base.toml"). Settings merge top-down.

Make config-driven choices first-class:

• Don't hardcode "max line 79". Let users override.
• Don't ship rules enabled by default that users will spend hours suppressing.
• Document each rule's purpose + how to fix.