Python

Python Core Knowledge

Full Reference: See advanced.md for production patterns: Result types, custom exceptions, structured logging, Pydantic validation, testing patterns, performance optimization, and dependency injection.

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: python for comprehensive documentation.

Python Version Support

Type Hints (Modern Syntax)

# Python 3.10+ - Use | instead of Union
def greet(name: str | None = None) -> str:
    return f"Hello, {name or 'World'}"

# Python 3.9+ - Use built-in generics
def process(items: list[str]) -> dict[str, int]:
    return {item: len(item) for item in items}

# Python 3.12+ - PEP 695 Type Parameter Syntax
def first[T](items: list[T]) -> T | None:
    return items[0] if items else None

class Stack[T]:
    def __init__(self) -> None:
        self._items: list[T] = []

    def push(self, item: T) -> None:
        self._items.append(item)

    def pop(self) -> T:
        return self._items.pop()

# Type aliases (Python 3.12+)
type Point = tuple[float, float]
type Vector[T] = list[T]
type Handler[T] = Callable[[T], None]

# Callable
def apply(fn: Callable[[int], int], value: int) -> int:
    return fn(value)

Dataclasses

from dataclasses import dataclass, field
from datetime import datetime

@dataclass
class User:
    id: int
    name: str
    email: str
    created_at: datetime = field(default_factory=datetime.now)
    is_active: bool = True

    def __post_init__(self):
        self.email = self.email.lower()

# Frozen (immutable)
@dataclass(frozen=True)
class Point:
    x: float
    y: float

# Slots for memory efficiency (Python 3.10+)
@dataclass(slots=True)
class Optimized:
    value: int

Async/Await

import asyncio
import aiohttp

async def fetch_user(id: int) -> dict:
    async with aiohttp.ClientSession() as session:
        async with session.get(f'/api/users/{id}') as response:
            return await response.json()

async def fetch_all_users(ids: List[int]) -> List[dict]:
    tasks = [fetch_user(id) for id in ids]
    return await asyncio.gather(*tasks)

# Run
asyncio.run(fetch_all_users([1, 2, 3]))

Context Managers

from contextlib import contextmanager, asynccontextmanager

@contextmanager
def timer():
    start = time.time()
    yield
    print(f"Elapsed: {time.time() - start:.2f}s")

with timer():
    process_data()

@asynccontextmanager
async def get_db():
    db = await create_connection()
    try:
        yield db
    finally:
        await db.close()

Modern Patterns

# Match (3.10+)
match status:
    case "active":
        handle_active()
    case "inactive" | "pending":
        handle_pending()
    case {"type": "user", "name": name}:  # Dict pattern
        handle_user(name)
    case [first, *rest]:  # Sequence pattern
        handle_sequence(first, rest)
    case _:
        handle_default()

# Walrus operator
if (n := len(items)) > 10:
    print(f"Too many: {n}")

# Exception groups (3.11+)
try:
    async with asyncio.TaskGroup() as tg:
        tg.create_task(task1())
        tg.create_task(task2())
except* ValueError as eg:
    for exc in eg.exceptions:
        print(f"ValueError: {exc}")
except* TypeError as eg:
    for exc in eg.exceptions:
        print(f"TypeError: {exc}")

Static Analysis & Linting

Official Rules References

Style Guides

Ruff Configuration

# pyproject.toml
[tool.ruff]
line-length = 88
target-version = "py312"

[tool.ruff.lint]
select = [
    "E",    # pycodestyle errors
    "W",    # pycodestyle warnings
    "F",    # Pyflakes
    "I",    # isort
    "B",    # flake8-bugbear
    "C4",   # flake8-comprehensions
    "UP",   # pyupgrade
    "S",    # flake8-bandit (security)
]
ignore = ["E501"]  # line too long (handled by formatter)

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

Full configuration guide: See python-quality skill

Key Rules Categories

When NOT to Use This Skill

Anti-Patterns

Quick Troubleshooting

Reference Documentation

• Typing - Type hints, generics, PEP 695
• Async - asyncio, TaskGroup, patterns
• CLI - Typer, Click, Rich
• Packaging - uv, poetry, pyproject.toml