python-code-style

name	python-code-style
description	Use when configuring ruff/mypy/pyright, setting up formatting, writing docstrings, or establishing coding standards. Do NOT use for general patterns (use python-patterns) or testing (use python-testing).
paths	**/*.py, **/pyproject.toml, **/setup.cfg, **/.flake8, **/mypy.ini

Python Code Style & Tooling

판단 기준과 규칙 중심. ruff/mypy 설정과 네이밍 규칙의 올바른 선택을 안내.

Quick Start

• 린터/포매터 설정? --> Ruff Config below
• 타입 체커 선택? --> Type Checker Decision below
• 네이밍 규칙? --> Naming Rules below
• 독스트링 작성? --> Docstring Rules below
• Ruff 룰 카테고리 상세? --> references/ruff-rules-guide.md

CRITICAL Rules

1. ALWAYS use ruff as single linter+formatter -- flake8+isort+black 조합 대체
2. ALWAYS enable strict mypy or pyright for production code
3. ALWAYS 120 char line length -- 현대 디스플레이 표준
4. ALWAYS absolute imports -- from mypackage.utils import x (relative imports 금지)
5. NEVER from module import * -- 명시적 import만
6. ALWAYS Google-style docstrings -- public API에 필수
7. PREFER ruff check --fix + ruff format -- 수동 포매팅 금지
8. ALWAYS configure per-file-ignores for tests -- S101(assert), ARG 허용
9. PREFER pyproject.toml 단일 설정 -- setup.cfg, .flake8 등 분산 금지

Type Checker Decision

Need type checking?
+-- New project, full control? --> pyright (strict mode, faster, LSP 내장)
+-- Existing project, gradual adoption? --> mypy (strict=true, overrides로 점진적)
+-- Both available? --> pyright (개발 시) + mypy (CI용)
+-- Django/SQLAlchemy project? --> mypy + django-stubs/sqlalchemy-stubs

mypy Config

[tool.mypy]
python_version = "3.12"
strict = true
warn_return_any = true
warn_unused_ignores = true

[[tool.mypy.overrides]]
module = "tests.*"
disallow_untyped_defs = false

pyright Config

[tool.pyright]
pythonVersion = "3.12"
typeCheckingMode = "strict"

Ruff Configuration

Strictness Levels

Level	select	Use Case
Minimal	E, W, F, I, B, UP	레거시 프로젝트, 빠른 도입
Standard	+ C4, SIM, PT, RET, RUF, PERF	신규 프로젝트 권장
Strict	ALL (with ignores)	최대 안전성, 라이브러리 개발

Standard Config (Recommended)

[tool.ruff]
line-length = 120
target-version = "py312"

[tool.ruff.lint]
select = [
    "E", "W", "F", "I", "B", "C4",
    "UP", "SIM", "PT", "RET", "RUF", "PERF",
]
ignore = ["E501"]  # formatter handles line length

[tool.ruff.lint.per-file-ignores]
"tests/**/*.py" = ["S101", "ARG", "PT004"]
"__init__.py" = ["F401"]

[tool.ruff.lint.isort]
known-first-party = ["mypackage"]

[tool.ruff.format]
quote-style = "double"
indent-style = "space"
docstring-code-format = true

Naming Rules

Element	Convention	Example
Module/file	snake_case	user_repository.py
Class	PascalCase	UserRepository
Function/variable	snake_case	get_user_by_email
Constant	SCREAMING_SNAKE_CASE	MAX_RETRY_ATTEMPTS
Type variable	PascalCase or single letter	T, KeyType
Private	_prefix	_internal_cache
Acronym in class	Uppercase	HTTPClientFactory

Naming Anti-Patterns

# BAD: Abbreviations
usr_repo.py, ord_proc.py, http_cli.py

# GOOD: Descriptive
user_repository.py, order_processing.py, http_client.py

# BAD: Generic names
data, info, result, temp, foo

# GOOD: Intent-revealing names
user_count, order_total, parsed_response

Docstring Rules

When to Write

Target	Required?
Public function/method	Yes -- 항상
Public class	Yes -- __init__ 포함
Private with complex logic	Yes
Trivial getter/setter	No -- 타입 힌트로 충분
Test function	No -- 함수명이 문서

Format (Google Style)

def process_batch(
    items: list[Item],
    max_workers: int = 4,
    on_progress: Callable[[int, int], None] | None = None,
) -> BatchResult:
    """Process items concurrently using a worker pool.

    Args:
        items: The items to process. Must not be empty.
        max_workers: Maximum concurrent workers. Defaults to 4.
        on_progress: Optional callback receiving (completed, total).

    Returns:
        BatchResult with succeeded items and failures.

    Raises:
        ValueError: If items is empty.
    """

Rules:

• 한 줄이면 """Retrieve a user by ID.""" (closing quotes 같은 줄)
• 복잡하면 summary line + blank line + details
• Args, Returns, Raises 순서 고정
• Example: 섹션은 doctest로 실행 가능하게

Import Organization

# 1. Standard library
import os
from collections.abc import Callable

# 2. Third-party
import httpx
from pydantic import BaseModel

# 3. Local (absolute imports only)
from myproject.models import User
from myproject.services import UserService

ruff의 I rule이 자동 정렬. known-first-party 설정 필수.

Anti-Patterns

Anti-Pattern	Problem	Fix
from module import *	네임스페이스 오염	명시적 import
from ..utils import x	리팩토링 시 깨짐	절대 import
print() for debugging	프로덕션에 남음	logging 또는 ruff T20 rule
Manual formatting	일관성 깨짐, 시간 낭비	ruff format 자동화
setup.cfg + .flake8 + .isort.cfg	설정 파일 분산	pyproject.toml 단일 파일
# type: ignore without code	어떤 에러인지 불명확	# type: ignore[specific-error]
noqa without code	어떤 룰인지 불명확	# noqa: E501 명시

Gotchas

• ❌ ruff에서 select = ["ALL"] → 너무 공격적, ["E", "F", "W", "I"]부터 시작
• ❌ mypy strict 모드 기존 프로젝트에 바로 적용 → 점진적 적용 필수
• ❌ docstring에 파라미터 타입 중복 기술 → type hints가 있으면 docstring에서 타입 생략

Troubleshooting

Symptom	Cause	Solution
ruff format과 lint 충돌	COM812, ISC001 rule 활성	ignore에 추가
mypy "missing stubs"	서드파티 타입 스텁 없음	pip install types-xxx 또는 [[tool.mypy.overrides]]
CI에서만 lint 실패	로컬 ruff 버전 차이	pre-commit 또는 CI에서 버전 고정
isort 정렬 안 맞음	known-first-party 미설정	ruff.lint.isort에 패키지명 추가

Cross-References

Topic	Skill
Python 패턴, 타입 힌트, 동시성	python-patterns
pytest, TDD, fixtures, mocking	python-testing
Ruff 룰 카테고리 전체, pre-commit 설정	references/ruff-rules-guide.md

References

• Ruff docs -- Official documentation
• Ruff rules -- Complete rule listing
• mypy docs -- Type checker
• pyright docs -- Microsoft type checker
• PEP 8 -- Python style guide
• PEP 257 -- Docstring conventions
• Google Python Style Guide