mirror of
https://github.com/affaan-m/everything-claude-code.git
synced 2026-03-30 21:53:28 +08:00
750 lines
17 KiB
Markdown
750 lines
17 KiB
Markdown
---
|
||
name: python-patterns
|
||
description: Pythonic イディオム、PEP 8標準、型ヒント、堅牢で効率的かつ保守可能なPythonアプリケーションを構築するためのベストプラクティス。
|
||
---
|
||
|
||
# Python開発パターン
|
||
|
||
堅牢で効率的かつ保守可能なアプリケーションを構築するための慣用的なPythonパターンとベストプラクティス。
|
||
|
||
## いつ有効化するか
|
||
|
||
- 新しいPythonコードを書くとき
|
||
- Pythonコードをレビューするとき
|
||
- 既存のPythonコードをリファクタリングするとき
|
||
- Pythonパッケージ/モジュールを設計するとき
|
||
|
||
## 核となる原則
|
||
|
||
### 1. 可読性が重要
|
||
|
||
Pythonは可読性を優先します。コードは明白で理解しやすいものであるべきです。
|
||
|
||
```python
|
||
# Good: Clear and readable
|
||
def get_active_users(users: list[User]) -> list[User]:
|
||
"""Return only active users from the provided list."""
|
||
return [user for user in users if user.is_active]
|
||
|
||
|
||
# Bad: Clever but confusing
|
||
def get_active_users(u):
|
||
return [x for x in u if x.a]
|
||
```
|
||
|
||
### 2. 明示的は暗黙的より良い
|
||
|
||
魔法を避け、コードが何をしているかを明確にしましょう。
|
||
|
||
```python
|
||
# Good: Explicit configuration
|
||
import logging
|
||
|
||
logging.basicConfig(
|
||
level=logging.INFO,
|
||
format='%(asctime)s - %(name)s - %(levelname)s - %(message)s'
|
||
)
|
||
|
||
# Bad: Hidden side effects
|
||
import some_module
|
||
some_module.setup() # What does this do?
|
||
```
|
||
|
||
### 3. EAFP - 許可を求めるより許しを請う方が簡単
|
||
|
||
Pythonは条件チェックよりも例外処理を好みます。
|
||
|
||
```python
|
||
# Good: EAFP style
|
||
def get_value(dictionary: dict, key: str) -> Any:
|
||
try:
|
||
return dictionary[key]
|
||
except KeyError:
|
||
return default_value
|
||
|
||
# Bad: LBYL (Look Before You Leap) style
|
||
def get_value(dictionary: dict, key: str) -> Any:
|
||
if key in dictionary:
|
||
return dictionary[key]
|
||
else:
|
||
return default_value
|
||
```
|
||
|
||
## 型ヒント
|
||
|
||
### 基本的な型アノテーション
|
||
|
||
```python
|
||
from typing import Optional, List, Dict, Any
|
||
|
||
def process_user(
|
||
user_id: str,
|
||
data: Dict[str, Any],
|
||
active: bool = True
|
||
) -> Optional[User]:
|
||
"""Process a user and return the updated User or None."""
|
||
if not active:
|
||
return None
|
||
return User(user_id, data)
|
||
```
|
||
|
||
### モダンな型ヒント（Python 3.9+）
|
||
|
||
```python
|
||
# Python 3.9+ - Use built-in types
|
||
def process_items(items: list[str]) -> dict[str, int]:
|
||
return {item: len(item) for item in items}
|
||
|
||
# Python 3.8 and earlier - Use typing module
|
||
from typing import List, Dict
|
||
|
||
def process_items(items: List[str]) -> Dict[str, int]:
|
||
return {item: len(item) for item in items}
|
||
```
|
||
|
||
### 型エイリアスとTypeVar
|
||
|
||
```python
|
||
from typing import TypeVar, Union
|
||
|
||
# Type alias for complex types
|
||
JSON = Union[dict[str, Any], list[Any], str, int, float, bool, None]
|
||
|
||
def parse_json(data: str) -> JSON:
|
||
return json.loads(data)
|
||
|
||
# Generic types
|
||
T = TypeVar('T')
|
||
|
||
def first(items: list[T]) -> T | None:
|
||
"""Return the first item or None if list is empty."""
|
||
return items[0] if items else None
|
||
```
|
||
|
||
### プロトコルベースのダックタイピング
|
||
|
||
```python
|
||
from typing import Protocol
|
||
|
||
class Renderable(Protocol):
|
||
def render(self) -> str:
|
||
"""Render the object to a string."""
|
||
|
||
def render_all(items: list[Renderable]) -> str:
|
||
"""Render all items that implement the Renderable protocol."""
|
||
return "\n".join(item.render() for item in items)
|
||
```
|
||
|
||
## エラーハンドリングパターン
|
||
|
||
### 特定の例外処理
|
||
|
||
```python
|
||
# Good: Catch specific exceptions
|
||
def load_config(path: str) -> Config:
|
||
try:
|
||
with open(path) as f:
|
||
return Config.from_json(f.read())
|
||
except FileNotFoundError as e:
|
||
raise ConfigError(f"Config file not found: {path}") from e
|
||
except json.JSONDecodeError as e:
|
||
raise ConfigError(f"Invalid JSON in config: {path}") from e
|
||
|
||
# Bad: Bare except
|
||
def load_config(path: str) -> Config:
|
||
try:
|
||
with open(path) as f:
|
||
return Config.from_json(f.read())
|
||
except:
|
||
return None # Silent failure!
|
||
```
|
||
|
||
### 例外の連鎖
|
||
|
||
```python
|
||
def process_data(data: str) -> Result:
|
||
try:
|
||
parsed = json.loads(data)
|
||
except json.JSONDecodeError as e:
|
||
# Chain exceptions to preserve the traceback
|
||
raise ValueError(f"Failed to parse data: {data}") from e
|
||
```
|
||
|
||
### カスタム例外階層
|
||
|
||
```python
|
||
class AppError(Exception):
|
||
"""Base exception for all application errors."""
|
||
pass
|
||
|
||
class ValidationError(AppError):
|
||
"""Raised when input validation fails."""
|
||
pass
|
||
|
||
class NotFoundError(AppError):
|
||
"""Raised when a requested resource is not found."""
|
||
pass
|
||
|
||
# Usage
|
||
def get_user(user_id: str) -> User:
|
||
user = db.find_user(user_id)
|
||
if not user:
|
||
raise NotFoundError(f"User not found: {user_id}")
|
||
return user
|
||
```
|
||
|
||
## コンテキストマネージャ
|
||
|
||
### リソース管理
|
||
|
||
```python
|
||
# Good: Using context managers
|
||
def process_file(path: str) -> str:
|
||
with open(path, 'r') as f:
|
||
return f.read()
|
||
|
||
# Bad: Manual resource management
|
||
def process_file(path: str) -> str:
|
||
f = open(path, 'r')
|
||
try:
|
||
return f.read()
|
||
finally:
|
||
f.close()
|
||
```
|
||
|
||
### カスタムコンテキストマネージャ
|
||
|
||
```python
|
||
from contextlib import contextmanager
|
||
|
||
@contextmanager
|
||
def timer(name: str):
|
||
"""Context manager to time a block of code."""
|
||
start = time.perf_counter()
|
||
yield
|
||
elapsed = time.perf_counter() - start
|
||
print(f"{name} took {elapsed:.4f} seconds")
|
||
|
||
# Usage
|
||
with timer("data processing"):
|
||
process_large_dataset()
|
||
```
|
||
|
||
### コンテキストマネージャクラス
|
||
|
||
```python
|
||
class DatabaseTransaction:
|
||
def __init__(self, connection):
|
||
self.connection = connection
|
||
|
||
def __enter__(self):
|
||
self.connection.begin_transaction()
|
||
return self
|
||
|
||
def __exit__(self, exc_type, exc_val, exc_tb):
|
||
if exc_type is None:
|
||
self.connection.commit()
|
||
else:
|
||
self.connection.rollback()
|
||
return False # Don't suppress exceptions
|
||
|
||
# Usage
|
||
with DatabaseTransaction(conn):
|
||
user = conn.create_user(user_data)
|
||
conn.create_profile(user.id, profile_data)
|
||
```
|
||
|
||
## 内包表記とジェネレータ
|
||
|
||
### リスト内包表記
|
||
|
||
```python
|
||
# Good: List comprehension for simple transformations
|
||
names = [user.name for user in users if user.is_active]
|
||
|
||
# Bad: Manual loop
|
||
names = []
|
||
for user in users:
|
||
if user.is_active:
|
||
names.append(user.name)
|
||
|
||
# Complex comprehensions should be expanded
|
||
# Bad: Too complex
|
||
result = [x * 2 for x in items if x > 0 if x % 2 == 0]
|
||
|
||
# Good: Use a generator function
|
||
def filter_and_transform(items: Iterable[int]) -> list[int]:
|
||
result = []
|
||
for x in items:
|
||
if x > 0 and x % 2 == 0:
|
||
result.append(x * 2)
|
||
return result
|
||
```
|
||
|
||
### ジェネレータ式
|
||
|
||
```python
|
||
# Good: Generator for lazy evaluation
|
||
total = sum(x * x for x in range(1_000_000))
|
||
|
||
# Bad: Creates large intermediate list
|
||
total = sum([x * x for x in range(1_000_000)])
|
||
```
|
||
|
||
### ジェネレータ関数
|
||
|
||
```python
|
||
def read_large_file(path: str) -> Iterator[str]:
|
||
"""Read a large file line by line."""
|
||
with open(path) as f:
|
||
for line in f:
|
||
yield line.strip()
|
||
|
||
# Usage
|
||
for line in read_large_file("huge.txt"):
|
||
process(line)
|
||
```
|
||
|
||
## データクラスと名前付きタプル
|
||
|
||
### データクラス
|
||
|
||
```python
|
||
from dataclasses import dataclass, field
|
||
from datetime import datetime
|
||
|
||
@dataclass
|
||
class User:
|
||
"""User entity with automatic __init__, __repr__, and __eq__."""
|
||
id: str
|
||
name: str
|
||
email: str
|
||
created_at: datetime = field(default_factory=datetime.now)
|
||
is_active: bool = True
|
||
|
||
# Usage
|
||
user = User(
|
||
id="123",
|
||
name="Alice",
|
||
email="alice@example.com"
|
||
)
|
||
```
|
||
|
||
### バリデーション付きデータクラス
|
||
|
||
```python
|
||
@dataclass
|
||
class User:
|
||
email: str
|
||
age: int
|
||
|
||
def __post_init__(self):
|
||
# Validate email format
|
||
if "@" not in self.email:
|
||
raise ValueError(f"Invalid email: {self.email}")
|
||
# Validate age range
|
||
if self.age < 0 or self.age > 150:
|
||
raise ValueError(f"Invalid age: {self.age}")
|
||
```
|
||
|
||
### 名前付きタプル
|
||
|
||
```python
|
||
from typing import NamedTuple
|
||
|
||
class Point(NamedTuple):
|
||
"""Immutable 2D point."""
|
||
x: float
|
||
y: float
|
||
|
||
def distance(self, other: 'Point') -> float:
|
||
return ((self.x - other.x) ** 2 + (self.y - other.y) ** 2) ** 0.5
|
||
|
||
# Usage
|
||
p1 = Point(0, 0)
|
||
p2 = Point(3, 4)
|
||
print(p1.distance(p2)) # 5.0
|
||
```
|
||
|
||
## デコレータ
|
||
|
||
### 関数デコレータ
|
||
|
||
```python
|
||
import functools
|
||
import time
|
||
|
||
def timer(func: Callable) -> Callable:
|
||
"""Decorator to time function execution."""
|
||
@functools.wraps(func)
|
||
def wrapper(*args, **kwargs):
|
||
start = time.perf_counter()
|
||
result = func(*args, **kwargs)
|
||
elapsed = time.perf_counter() - start
|
||
print(f"{func.__name__} took {elapsed:.4f}s")
|
||
return result
|
||
return wrapper
|
||
|
||
@timer
|
||
def slow_function():
|
||
time.sleep(1)
|
||
|
||
# slow_function() prints: slow_function took 1.0012s
|
||
```
|
||
|
||
### パラメータ化デコレータ
|
||
|
||
```python
|
||
def repeat(times: int):
|
||
"""Decorator to repeat a function multiple times."""
|
||
def decorator(func: Callable) -> Callable:
|
||
@functools.wraps(func)
|
||
def wrapper(*args, **kwargs):
|
||
results = []
|
||
for _ in range(times):
|
||
results.append(func(*args, **kwargs))
|
||
return results
|
||
return wrapper
|
||
return decorator
|
||
|
||
@repeat(times=3)
|
||
def greet(name: str) -> str:
|
||
return f"Hello, {name}!"
|
||
|
||
# greet("Alice") returns ["Hello, Alice!", "Hello, Alice!", "Hello, Alice!"]
|
||
```
|
||
|
||
### クラスベースのデコレータ
|
||
|
||
```python
|
||
class CountCalls:
|
||
"""Decorator that counts how many times a function is called."""
|
||
def __init__(self, func: Callable):
|
||
functools.update_wrapper(self, func)
|
||
self.func = func
|
||
self.count = 0
|
||
|
||
def __call__(self, *args, **kwargs):
|
||
self.count += 1
|
||
print(f"{self.func.__name__} has been called {self.count} times")
|
||
return self.func(*args, **kwargs)
|
||
|
||
@CountCalls
|
||
def process():
|
||
pass
|
||
|
||
# Each call to process() prints the call count
|
||
```
|
||
|
||
## 並行処理パターン
|
||
|
||
### I/Oバウンドタスク用のスレッド
|
||
|
||
```python
|
||
import concurrent.futures
|
||
import threading
|
||
|
||
def fetch_url(url: str) -> str:
|
||
"""Fetch a URL (I/O-bound operation)."""
|
||
import urllib.request
|
||
with urllib.request.urlopen(url) as response:
|
||
return response.read().decode()
|
||
|
||
def fetch_all_urls(urls: list[str]) -> dict[str, str]:
|
||
"""Fetch multiple URLs concurrently using threads."""
|
||
with concurrent.futures.ThreadPoolExecutor(max_workers=10) as executor:
|
||
future_to_url = {executor.submit(fetch_url, url): url for url in urls}
|
||
results = {}
|
||
for future in concurrent.futures.as_completed(future_to_url):
|
||
url = future_to_url[future]
|
||
try:
|
||
results[url] = future.result()
|
||
except Exception as e:
|
||
results[url] = f"Error: {e}"
|
||
return results
|
||
```
|
||
|
||
### CPUバウンドタスク用のマルチプロセシング
|
||
|
||
```python
|
||
def process_data(data: list[int]) -> int:
|
||
"""CPU-intensive computation."""
|
||
return sum(x ** 2 for x in data)
|
||
|
||
def process_all(datasets: list[list[int]]) -> list[int]:
|
||
"""Process multiple datasets using multiple processes."""
|
||
with concurrent.futures.ProcessPoolExecutor() as executor:
|
||
results = list(executor.map(process_data, datasets))
|
||
return results
|
||
```
|
||
|
||
### 並行I/O用のAsync/Await
|
||
|
||
```python
|
||
import asyncio
|
||
|
||
async def fetch_async(url: str) -> str:
|
||
"""Fetch a URL asynchronously."""
|
||
import aiohttp
|
||
async with aiohttp.ClientSession() as session:
|
||
async with session.get(url) as response:
|
||
return await response.text()
|
||
|
||
async def fetch_all(urls: list[str]) -> dict[str, str]:
|
||
"""Fetch multiple URLs concurrently."""
|
||
tasks = [fetch_async(url) for url in urls]
|
||
results = await asyncio.gather(*tasks, return_exceptions=True)
|
||
return dict(zip(urls, results))
|
||
```
|
||
|
||
## パッケージ構成
|
||
|
||
### 標準プロジェクトレイアウト
|
||
|
||
```
|
||
myproject/
|
||
├── src/
|
||
│ └── mypackage/
|
||
│ ├── __init__.py
|
||
│ ├── main.py
|
||
│ ├── api/
|
||
│ │ ├── __init__.py
|
||
│ │ └── routes.py
|
||
│ ├── models/
|
||
│ │ ├── __init__.py
|
||
│ │ └── user.py
|
||
│ └── utils/
|
||
│ ├── __init__.py
|
||
│ └── helpers.py
|
||
├── tests/
|
||
│ ├── __init__.py
|
||
│ ├── conftest.py
|
||
│ ├── test_api.py
|
||
│ └── test_models.py
|
||
├── pyproject.toml
|
||
├── README.md
|
||
└── .gitignore
|
||
```
|
||
|
||
### インポート規約
|
||
|
||
```python
|
||
# Good: Import order - stdlib, third-party, local
|
||
import os
|
||
import sys
|
||
from pathlib import Path
|
||
|
||
import requests
|
||
from fastapi import FastAPI
|
||
|
||
from mypackage.models import User
|
||
from mypackage.utils import format_name
|
||
|
||
# Good: Use isort for automatic import sorting
|
||
# pip install isort
|
||
```
|
||
|
||
### パッケージエクスポート用の__init__.py
|
||
|
||
```python
|
||
# mypackage/__init__.py
|
||
"""mypackage - A sample Python package."""
|
||
|
||
__version__ = "1.0.0"
|
||
|
||
# Export main classes/functions at package level
|
||
from mypackage.models import User, Post
|
||
from mypackage.utils import format_name
|
||
|
||
__all__ = ["User", "Post", "format_name"]
|
||
```
|
||
|
||
## メモリとパフォーマンス
|
||
|
||
### メモリ効率化のための__slots__使用
|
||
|
||
```python
|
||
# Bad: Regular class uses __dict__ (more memory)
|
||
class Point:
|
||
def __init__(self, x: float, y: float):
|
||
self.x = x
|
||
self.y = y
|
||
|
||
# Good: __slots__ reduces memory usage
|
||
class Point:
|
||
__slots__ = ['x', 'y']
|
||
|
||
def __init__(self, x: float, y: float):
|
||
self.x = x
|
||
self.y = y
|
||
```
|
||
|
||
### 大量データ用のジェネレータ
|
||
|
||
```python
|
||
# Bad: Returns full list in memory
|
||
def read_lines(path: str) -> list[str]:
|
||
with open(path) as f:
|
||
return [line.strip() for line in f]
|
||
|
||
# Good: Yields lines one at a time
|
||
def read_lines(path: str) -> Iterator[str]:
|
||
with open(path) as f:
|
||
for line in f:
|
||
yield line.strip()
|
||
```
|
||
|
||
### ループ内での文字列連結を避ける
|
||
|
||
```python
|
||
# Bad: O(n²) due to string immutability
|
||
result = ""
|
||
for item in items:
|
||
result += str(item)
|
||
|
||
# Good: O(n) using join
|
||
result = "".join(str(item) for item in items)
|
||
|
||
# Good: Using StringIO for building
|
||
from io import StringIO
|
||
|
||
buffer = StringIO()
|
||
for item in items:
|
||
buffer.write(str(item))
|
||
result = buffer.getvalue()
|
||
```
|
||
|
||
## Pythonツール統合
|
||
|
||
### 基本コマンド
|
||
|
||
```bash
|
||
# Code formatting
|
||
black .
|
||
isort .
|
||
|
||
# Linting
|
||
ruff check .
|
||
pylint mypackage/
|
||
|
||
# Type checking
|
||
mypy .
|
||
|
||
# Testing
|
||
pytest --cov=mypackage --cov-report=html
|
||
|
||
# Security scanning
|
||
bandit -r .
|
||
|
||
# Dependency management
|
||
pip-audit
|
||
safety check
|
||
```
|
||
|
||
### pyproject.toml設定
|
||
|
||
```toml
|
||
[project]
|
||
name = "mypackage"
|
||
version = "1.0.0"
|
||
requires-python = ">=3.9"
|
||
dependencies = [
|
||
"requests>=2.31.0",
|
||
"pydantic>=2.0.0",
|
||
]
|
||
|
||
[project.optional-dependencies]
|
||
dev = [
|
||
"pytest>=7.4.0",
|
||
"pytest-cov>=4.1.0",
|
||
"black>=23.0.0",
|
||
"ruff>=0.1.0",
|
||
"mypy>=1.5.0",
|
||
]
|
||
|
||
[tool.black]
|
||
line-length = 88
|
||
target-version = ['py39']
|
||
|
||
[tool.ruff]
|
||
line-length = 88
|
||
select = ["E", "F", "I", "N", "W"]
|
||
|
||
[tool.mypy]
|
||
python_version = "3.9"
|
||
warn_return_any = true
|
||
warn_unused_configs = true
|
||
disallow_untyped_defs = true
|
||
|
||
[tool.pytest.ini_options]
|
||
testpaths = ["tests"]
|
||
addopts = "--cov=mypackage --cov-report=term-missing"
|
||
```
|
||
|
||
## クイックリファレンス：Pythonイディオム
|
||
|
||
| イディオム | 説明 |
|
||
|-------|-------------|
|
||
| EAFP | 許可を求めるより許しを請う方が簡単 |
|
||
| コンテキストマネージャ | リソース管理には`with`を使用 |
|
||
| リスト内包表記 | 簡単な変換用 |
|
||
| ジェネレータ | 遅延評価と大規模データセット用 |
|
||
| 型ヒント | 関数シグネチャへのアノテーション |
|
||
| データクラス | 自動生成メソッド付きデータコンテナ用 |
|
||
| `__slots__` | メモリ最適化用 |
|
||
| f-strings | 文字列フォーマット用（Python 3.6+） |
|
||
| `pathlib.Path` | パス操作用（Python 3.4+） |
|
||
| `enumerate` | ループ内のインデックス-要素ペア用 |
|
||
|
||
## 避けるべきアンチパターン
|
||
|
||
```python
|
||
# Bad: Mutable default arguments
|
||
def append_to(item, items=[]):
|
||
items.append(item)
|
||
return items
|
||
|
||
# Good: Use None and create new list
|
||
def append_to(item, items=None):
|
||
if items is None:
|
||
items = []
|
||
items.append(item)
|
||
return items
|
||
|
||
# Bad: Checking type with type()
|
||
if type(obj) == list:
|
||
process(obj)
|
||
|
||
# Good: Use isinstance
|
||
if isinstance(obj, list):
|
||
process(obj)
|
||
|
||
# Bad: Comparing to None with ==
|
||
if value == None:
|
||
process()
|
||
|
||
# Good: Use is
|
||
if value is None:
|
||
process()
|
||
|
||
# Bad: from module import *
|
||
from os.path import *
|
||
|
||
# Good: Explicit imports
|
||
from os.path import join, exists
|
||
|
||
# Bad: Bare except
|
||
try:
|
||
risky_operation()
|
||
except:
|
||
pass
|
||
|
||
# Good: Specific exception
|
||
try:
|
||
risky_operation()
|
||
except SpecificError as e:
|
||
logger.error(f"Operation failed: {e}")
|
||
```
|
||
|
||
**覚えておいてください**: Pythonコードは読みやすく、明示的で、最小の驚きの原則に従うべきです。迷ったときは、巧妙さよりも明確さを優先してください。
|