Ruff Rule Categories — Purpose & Reason**

Ruff organizes linting rules into families (prefix codes like F, E, W, N, B, etc.). Here is the full high-level list.
Author

Benedict Thekkel

1. Pyflakes (F)

Purpose: Catch syntax errors, unused variables, undefined names. Reason: Prevents runtime crashes and dead code.

Examples

  • F401 — unused import
  • F821 — undefined variable
  • F841 — assigned but unused variable

2. pycodestyle (E, W)

Purpose: Enforce PEP 8 style and whitespace rules. Reason: Improves consistency/reliability across teams.

Examples

  • E501 — line too long
  • E302 — expected 2 blank lines
  • W291 — trailing whitespace

3. Pep8-naming (N)

Purpose: Ensure correct naming conventions. Reason: Makes code predictable.

Examples

  • N802 — function name should be lowercase
  • N803 — argument name should be lowercase
  • N806 — variable in function should be lowercase

4. pyupgrade (UP)

Purpose: Modernize code to newer Python syntax. Reason: Removes legacy patterns and ensures performance.

Examples

  • rewrite dict() → {}
  • rewrite .format() → f-string
  • replace old typing.X with built-in types (Python 3.9+)

5. Flake8-bugbear (B)

Purpose: Prevent common logic bugs. Reason: Catches subtle issues that tests often miss.

Examples

  • B006 — mutable default arguments
  • B007 — loop variable overwritten
  • B008 — function call in default argument

6. Flake8-comprehensions (C4)

Purpose: Improve comprehensions. Reason: Cleaner, faster, more Pythonic code.

Examples

  • C401 — unnecessary list/dict/set comprehension
  • C402 — unnecessary dict comprehension

7. isort (I)

Purpose: Sort imports automatically. Reason: Prevents merge conflicts and keeps imports consistent.

Examples:

  • I001 — imports not sorted

8. mccabe (C90)

Purpose: Check cyclomatic complexity. Reason: Flags overly complex functions → refactor opportunities.

Example:

  • C901 — function too complex

9. Pylint rules (PL)

Purpose: High-level code smell detection. Reason: Improves maintainability.

Examples:

  • PLR2004 — magic values
  • PLR0913 — too many arguments

10. Bandit (S)

Purpose: Security linting. Reason: Prevents real-world vulnerabilities.

Examples:

  • S102 — use of exec
  • S307 — suspicious use of eval
  • S501 — insecure requests call without verify

11. Flake8-boolean-trap (FBT)

Purpose: Avoid boolean default arguments. Reason: They hide poor API design.

Examples:

  • FBT001 — boolean default in function

12. Flake8-datetimez (DTZ)

Purpose: Enforce timezone-aware datetimes. Reason: Prevents timezone bugs (critical for Django).

Examples:

  • DTZ003 — datetime.now() used without timezone

13. Flake8-erase (ERA)

Purpose: Remove commented-out code blocks. Reason: Prevents stale code, improves readability.

Example:

  • ERA001 — commented-out code detected

14. Flake8-unused-arguments (ARG)

Purpose: Find unused function parameters. Reason: Often indicates dead code or refactoring leftovers.

Example:

  • ARG001 — unused function argument

15. Flake8-print (T20)

Purpose: Detect print statements. Reason: Prevents debug prints from leaking into prod.

Example:

  • T201 — print() found

16. Flake8-self (SLF)

Purpose: Prevent private attribute access. Reason: Encourages proper encapsulation.

Example:

  • SLF001 — accessing _private attribute

17. Flake8-type-checking (TC)

Purpose: Move heavy imports under TYPE_CHECKING. Reason: Faster runtime & avoids circular imports.

Example:

  • TC001 — move import into type-checking block

18. Flake8-ellipsis (PLE)

Purpose: Validate correct use of .... Reason: Avoids odd “placeholder” errors.

Example:

  • misuse of bare ellipsis

19. Tryceratops (TRY)

Purpose: Improve error handling. Reason: Prevents try/except anti-patterns.

Examples:

  • TRY002 — raise without from
  • TRY003 — too broad exception clause

20. Ruff-specific rules (RUF)

Purpose: Ruff’s own logic checks. Reason: Improves performance and sanity of code.

Examples:

  • RUF100 — unused noqa tag
  • RUF200 — ambiguous unicode character

21. Django rules (DJ)

(Only if Django plugin enabled) Purpose: Enforce Django best practices. Reason: Prevent ORM bugs and bad patterns.

Examples:

  • avoiding raw SQL
  • warning about null=True on CharField

22. Django security (DJ S)

Purpose: Catch common Django security issues. Reason: Prevents XSS, CSRF, password handling issues.

23. Pandas rules (PD) (new)

Purpose: Detect inefficient Pandas operations. Reason: Prevent memory/time blowouts.

Examples:

  • iterating rows unnecessarily
  • chained indexing

24. Async rules (ASYNC)

Purpose: Catch misuse of async/await. Reason: Ensures correct concurrency behavior.

Example:

  • blocking calls inside async functions

25. Typing rules (TYP)

Purpose: Improve annotations. Reason: Cleaner type hints → fewer mypy/pydantic errors.

Examples:

  • unnecessary Optional
  • improper Union[...] usage

26. Formatter rules (Ruff Formatter)

Purpose: Replace Black. Reason: Fastest Python formatter (2–5× faster).

Examples:

  • consistent string quotes
  • consistent docstring formatting

✔ Summary Table

Category Prefix Purpose
Pyflakes F Syntax / unused checks
pycodestyle E/W PEP 8 rules
pep8-naming N Naming rules
pyupgrade UP Modern Python
Flake8-bugbear B Logic bugs
Flake8-comprehensions C4 Comprehension improvements
isort I Import sorting
mccabe C90 Complexity
Pylint subset PL Code smells
Bandit S Security
Boolean trap FBT Boolean argument API issues
Datetimez DTZ TZ-safe datetimes
Erase ERA Remove commented code
Unused arguments ARG Unused parameters
Print statements T20 Remove debug prints
Self rules SLF Accessing private attrs
Type-checking TC Move imports
Tryceratops TRY Better try/except patterns
Ruff-specific RUF Internal checks
Django DJ Django practices
Pandas PD Pandas correctness/performance

If you want, I can also generate:

✅ A recommended Ruff configuration for your Django/DRF/pytest codebase ✅ A full ruff.toml template ✅ A diagram showing how rule categories overlap ✅ A priority list (rules to enable first, optional ones, strict mode)

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