FastAPI Python Pro

A scaffolding and code-assist skill for building production async APIs with FastAPI, Pydantic v2, and SQLAlchemy 2.0. It wires up the parts that are fiddly to assemble by hand — async session management, typed request/response models, JWT auth, and Alembic migrations — so you start from a working, idiomatic project instead of a blank main.py. Aimed at backend and full-stack developers who want correct async patterns rather than copy-pasted snippets that block the event loop.

When to use it

• Starting a new service and you want a sane layout (routers/, models/, schemas/, deps.py) from the first commit.
• Adding async database access with SQLAlchemy 2.0's async_sessionmaker and AsyncSession without leaking sessions across requests.
• Bolting JWT login onto an existing app, or migrating Pydantic v1 models to v2.
• You keep getting greenlet_spawn errors or "this session is already flushing" and need the dependency lifecycle done right.

What it does

• Generates Pydantic v2 schemas using model_config = ConfigDict(from_attributes=True), Field constraints, and field_validator / model_validator — not the deprecated v1 Config class or @validator.
• Sets up async SQLAlchemy with create_async_engine, DeclarativeBase, and Mapped[...] / mapped_column() typed models.
• Provides a get_db() dependency yielding an AsyncSession, injected via Depends(), and an OAuth2PasswordBearer flow issuing JWTs (python-jose + passlib/bcrypt).
• Initializes Alembic (alembic init, env.py pointed at your async engine) and writes the first autogenerated revision.
• OpenAPI docs come free at /docs and /redoc from your typed signatures.

Example

curl -fsSL --create-dirs -o ~/.claude/skills/fastapi-python-pro/SKILL.md https://claudeskil.com/skills/fastapi-python-pro/SKILL.md

# then, in your project:
"Scaffold a FastAPI app with a User model, async Postgres,
 JWT auth, and an Alembic baseline migration."

Generated route:

@router.get("/users/{user_id}", response_model=UserRead)
async def read_user(user_id: int, db: AsyncSession = Depends(get_db)):
    user = await db.get(User, user_id)
    if user is None:
        raise HTTPException(404, "User not found")
    return user

Tips & gotchas

• Define get_db with async with async_sessionmaker() as session: yield session — never share one session across requests.
• Set expire_on_commit=False on the sessionmaker, or attributes become un-awaited and detached after commit.
• Alembic autogenerate needs your models imported into env.py's target_metadata, and the async engine wrapped with run_sync in run_migrations_online.
• Use await db.execute(select(...)) then .scalars(); the old db.query() API is removed in 2.0 style.

FAQ

Does it require Postgres? No — defaults to asyncpg/Postgres but works with aiosqlite for local dev; swap the DATABASE_URL.

Pydantic v1 or v2? Strictly v2 (ConfigDict, model_dump(), Annotated fields). It can help port v1 code.

Can I run sync DB drivers? Possible, but the scaffold assumes async; mixing sync drivers under async routes will block the loop.