just-works: Skill for Claude Code

Python Coding

Project conventions override these defaults. Read 2-3 nearby modules and pyproject.toml (Python target, linter, tooling) before writing.

Never rules

• Never except: pass, and never a broad except Exception without re-raise or logging. Catch specific types; a broad catch makes a typo-induced KeyError look like a network failure.
• Never use naive datetimes. datetime.now() and datetime.utcnow() (deprecated since 3.12) return naive values. Use datetime.now(tz=timezone.utc), and zoneinfo.ZoneInfo rather than pytz for other zones.
• Never random for tokens, keys, or session IDs. Use secrets.
• Never shell=True when any argument can contain external input. Pass an argument list.
• Never trust external input in parsers or queries. Parameterize SQL instead of formatting strings, use yaml.safe_load, never pickle.load untrusted data, and never eval/exec external input (ast.literal_eval for literals).
• Never block the event loop in async def. No time.sleep(), requests, or synchronous file I/O. Use asyncio.sleep(), httpx, or asyncio.to_thread().

Error handling

Re-raise at I/O boundaries with raise ... from e to keep the original traceback. Use from None only when the cause is irrelevant to the caller. Define custom exception types when callers must tell failure modes apart.

try:
    result = await db.fetchrow("SELECT * FROM users WHERE id = $1", user_id)
except asyncpg.PostgresError as e:
    raise DatabaseError(f"Failed to query user {user_id}") from e

Log a caught exception with its traceback: logger.exception("API call failed") inside the except block, or exc_info=True at lower levels. logger.error(f"...{e}") loses the traceback.

Resource cleanup

Use a context manager (or finally) for every client, connection pool, and file handle; never create httpx.AsyncClient() or a pool bare. Use AsyncExitStack when entering several async resources in one function.