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Python Fastapi

aiskillstore/python-fastapi

Python FastAPI development with uv package manager, modular project structure, SQLAlchemy ORM, and production-ready patterns.

This is a copy. The original lives at comeonoliver/python-fastapi.

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Install

one command, takes just this skill from the repository
npx skills add https://github.com/aiskillstore/marketplace --skill python-fastapi

What comes with it

69 482 bytes besides the instruction
skill-report.json

The instruction itself

25 sections, as written by the author

Python FastAPI Development

Expert patterns for building Python APIs with FastAPI, uv package manager, modular architecture, and SQLAlchemy database integration.

Technology Stack

  • Runtime: Python 3.12+
  • Package Manager: uv (fast, Rust-based)
  • Framework: FastAPI
  • ORM: SQLAlchemy 2.0 (async)
  • Validation: Pydantic v2
  • Database: PostgreSQL (or SQLite for dev)
  • Migrations: Alembic
  • Testing: pytest, pytest-asyncio
  • Linting: ruff

Project Structure

Feature-based modular architecture - code organized by domain, not by layer:

my-project/
├── pyproject.toml           # Project config with uv
├── uv.lock                   # Lock file
├── .python-version           # Python version
├── .env                      # Environment variables
├── .env.example
├── alembic.ini               # Alembic config
├── alembic/                  # Migrations
│   ├── env.py
│   ├── script.py.mako
│   └── versions/
├── src/
│   └── app/
│       ├── __init__.py
│       ├── main.py           # FastAPI app entry
│       ├── config.py         # Settings
│       ├── database.py       # DB session
│       ├── core/
│       │   ├── __init__.py
│       │   ├── dependencies.py  # Shared dependencies
│       │   ├── exceptions.py    # Custom exceptions
│       │   ├── middleware.py    # Middleware
│       │   └── security.py      # Auth utilities
│       ├── models/
│       │   ├── __init__.py
│       │   └── base.py          # SQLAlchemy base & mixins
│       ├── features/
│       │   ├── __init__.py
│       │   ├── auth/
│       │   │   ├── __init__.py
│       │   │   ├── api.py       # Auth endpoints
│       │   │   ├── schemas.py   # Auth Pydantic schemas
│       │   │   ├── services.py  # Auth business logic
│       │   │   ├── models.py    # Auth SQLAlchemy models
│       │   │   └── utils.py     # Auth helpers (JWT, etc.)
│       │   ├── users/
│       │   │   ├── __init__.py
│       │   │   ├── api.py       # User endpoints
│       │   │   ├── schemas.py   # User Pydantic schemas
│       │   │   ├── services.py  # User business logic
│       │   │   ├── models.py    # User SQLAlchemy models
│       │   │   └── repository.py # User data access
│       │   └── items/
│       │       ├── __init__.py
│       │       ├── api.py
│       │       ├── schemas.py
│       │       ├── services.py
│       │       └── models.py
│       └── api/
│           ├── __init__.py
│           └── router.py        # Aggregates all feature routers
└── tests/
    ├── __init__.py
    ├── conftest.py
    ├── features/
    │   ├── auth/
    │   │   └── test_auth.py
    │   └── users/
    │       └── test_users.py
    └── integration/

Quick Setup with uv

# Install uv
curl -LsSf https://astral.sh/uv/install.sh | sh

# Create new project
uv init my-project
cd my-project

# Set Python version
uv python pin 3.12

# Add dependencies
uv add fastapi uvicorn[standard] sqlalchemy[asyncio] asyncpg
uv add pydantic pydantic-settings python-dotenv
uv add alembic

# Add dev dependencies
uv add --dev pytest pytest-asyncio pytest-cov httpx ruff mypy

# Create source structure
mkdir -p src/app/{api/v1/endpoints,core,models,schemas,services,repositories}
touch src/app/__init__.py

Core Patterns

pyproject.toml

[project]
name = "my-project"
version = "0.1.0"
description = "FastAPI application"
requires-python = ">=3.12"
dependencies = [
    "fastapi>=0.115.0",
    "uvicorn[standard]>=0.32.0",
    "sqlalchemy[asyncio]>=2.0.0",
    "asyncpg>=0.30.0",
    "pydantic>=2.10.0",
    "pydantic-settings>=2.6.0",
    "python-dotenv>=1.0.0",
    "alembic>=1.14.0",
]

[project.optional-dependencies]
dev = [
    "pytest>=8.0.0",
    "pytest-asyncio>=0.24.0",
    "pytest-cov>=6.0.0",
    "httpx>=0.28.0",
    "ruff>=0.8.0",
    "mypy>=1.13.0",
]

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

[tool.ruff.lint]
select = ["E", "F", "I", "N", "W", "UP", "B", "C4", "SIM"]

[tool.pytest.ini_options]
asyncio_mode = "auto"
testpaths = ["tests"]

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

Configuration (src/app/config.py)

from functools import lru_cache
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(
        env_file=".env",
        env_file_encoding="utf-8",
        case_sensitive=False,
    )

    # App
    app_name: str = "My API"
    debug: bool = False
    api_v1_prefix: str = "/api/v1"

    # Database
    database_url: str = "postgresql+asyncpg://user:pass@localhost:5432/db"

    # Security
    secret_key: str = "change-me-in-production"
    access_token_expire_minutes: int = 30


@lru_cache
def get_settings() -> Settings:
    return Settings()


settings = get_settings()

Database Setup (src/app/database.py)

from collections.abc import AsyncGenerator
from sqlalchemy.ext.asyncio import (
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)

from app.config import settings

engine = create_async_engine(
    settings.database_url,
    echo=settings.debug,
    pool_pre_ping=True,
)

async_session_maker = async_sessionmaker(
    engine,
    class_=AsyncSession,
    expire_on_commit=False,
)


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    async with async_session_maker() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise

SQLAlchemy Base Model (src/app/models/base.py)

from datetime import datetime
from sqlalchemy import DateTime, func
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column


class Base(DeclarativeBase):
    pass


class TimestampMixin:
    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True),
        server_default=func.now(),
    )
    updated_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True),
        server_default=func.now(),
        onupdate=func.now(),
    )

Feature Module Pattern

Each feature is self-contained with its own api, schemas, services, models, and utils.

Feature: users/schemas.py

from pydantic import BaseModel, EmailStr, ConfigDict


class UserBase(BaseModel):
    email: EmailStr
    full_name: str | None = None


class UserCreate(UserBase):
    password: str


class UserUpdate(BaseModel):
    email: EmailStr | None = None
    full_name: str | None = None
    password: str | None = None


class UserResponse(UserBase):
    model_config = ConfigDict(from_attributes=True)
    id: int
    is_active: bool

Feature: users/models.py

from sqlalchemy import String
from sqlalchemy.orm import Mapped, mapped_column

from app.models.base import Base, TimestampMixin


class User(Base, TimestampMixin):
    __tablename__ = "users"

    id: Mapped[int] = mapped_column(primary_key=True)
    email: Mapped[str] = mapped_column(String(255), unique=True, index=True)
    hashed_password: Mapped[str] = mapped_column(String(255))
    full_name: Mapped[str | None] = mapped_column(String(255))
    is_active: Mapped[bool] = mapped_column(default=True)

Feature: users/repository.py

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.features.users.models import User


class UserRepository:
    def __init__(self, db: AsyncSession):
        self.db = db

    async def get(self, id: int) -> User | None:
        result = await self.db.execute(select(User).where(User.id == id))
        return result.scalar_one_or_none()

    async def get_by_email(self, email: str) -> User | None:
        result = await self.db.execute(select(User).where(User.email == email))
        return result.scalar_one_or_none()

    async def get_all(self, skip: int = 0, limit: int = 100) -> list[User]:
        result = await self.db.execute(select(User).offset(skip).limit(limit))
        return list(result.scalars().all())

    async def create(self, data: dict) -> User:
        user = User(**data)
        self.db.add(user)
        await self.db.flush()
        await self.db.refresh(user)
        return user

    async def update(self, user: User, data: dict) -> User:
        for field, value in data.items():
            if value is not None:
                setattr(user, field, value)
        await self.db.flush()
        await self.db.refresh(user)
        return user

Feature: users/services.py

from sqlalchemy.ext.asyncio import AsyncSession

from app.core.security import hash_password
from app.features.users.models import User
from app.features.users.repository import UserRepository
from app.features.users.schemas import UserCreate, UserUpdate


class UserService:
    def __init__(self, db: AsyncSession):
        self.db = db
        self.repo = UserRepository(db)

    async def get(self, user_id: int) -> User | None:
        return await self.repo.get(user_id)

    async def get_by_email(self, email: str) -> User | None:
        return await self.repo.get_by_email(email)

    async def list(self, skip: int = 0, limit: int = 100) -> list[User]:
        return await self.repo.get_all(skip=skip, limit=limit)

    async def create(self, user_in: UserCreate) -> User:
        data = user_in.model_dump()
        data["hashed_password"] = hash_password(data.pop("password"))
        return await self.repo.create(data)

    async def update(self, user: User, user_in: UserUpdate) -> User:
        data = user_in.model_dump(exclude_unset=True)
        if "password" in data:
            data["hashed_password"] = hash_password(data.pop("password"))
        return await self.repo.update(user, data)

Feature: users/api.py

from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.ext.asyncio import AsyncSession

from app.database import get_db
from app.features.users.schemas import UserCreate, UserResponse, UserUpdate
from app.features.users.services import UserService

router = APIRouter(prefix="/users", tags=["users"])


def get_service(db: AsyncSession = Depends(get_db)) -> UserService:
    return UserService(db)


@router.get("", response_model=list[UserResponse])
async def list_users(
    skip: int = 0,
    limit: int = 100,
    service: UserService = Depends(get_service),
):
    return await service.list(skip=skip, limit=limit)


@router.get("/{user_id}", response_model=UserResponse)
async def get_user(
    user_id: int,
    service: UserService = Depends(get_service),
):
    user = await service.get(user_id)
    if not user:
        raise HTTPException(status_code=404, detail="User not found")
    return user


@router.post("", response_model=UserResponse, status_code=status.HTTP_201_CREATED)
async def create_user(
    user_in: UserCreate,
    service: UserService = Depends(get_service),
):
    if await service.get_by_email(user_in.email):
        raise HTTPException(status_code=400, detail="Email already registered")
    return await service.create(user_in)


@router.patch("/{user_id}", response_model=UserResponse)
async def update_user(
    user_id: int,
    user_in: UserUpdate,
    service: UserService = Depends(get_service),
):
    user = await service.get(user_id)
    if not user:
        raise HTTPException(status_code=404, detail="User not found")
    return await service.update(user, user_in)

Feature: users/__init__.py (exports)

from app.features.users.api import router
from app.features.users.models import User
from app.features.users.schemas import UserCreate, UserResponse, UserUpdate
from app.features.users.services import UserService

__all__ = ["router", "User", "UserCreate", "UserResponse", "UserUpdate", "UserService"]

Main Router (src/app/api/router.py)

from fastapi import APIRouter

from app.features.auth import router as auth_router
from app.features.users import router as users_router
from app.features.items import router as items_router

api_router = APIRouter()
api_router.include_router(auth_router)
api_router.include_router(users_router)
api_router.include_router(items_router)

FastAPI App (src/app/main.py)

from contextlib import asynccontextmanager
from collections.abc import AsyncIterator

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

from app.api.router import api_router
from app.config import settings
from app.database import engine


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncIterator[None]:
    # Startup
    yield
    # Shutdown
    await engine.dispose()


app = FastAPI(
    title=settings.app_name,
    openapi_url=f"{settings.api_v1_prefix}/openapi.json",
    lifespan=lifespan,
)

app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],  # Configure for production
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

app.include_router(api_router, prefix=settings.api_v1_prefix)


@app.get("/health")
async def health_check():
    return {"status": "healthy"}

Database Migrations with Alembic

# Initialize Alembic
uv run alembic init alembic

# Update alembic/env.py for async
# Then create migration
uv run alembic revision --autogenerate -m "Initial migration"

# Apply migrations
uv run alembic upgrade head

Async Alembic env.py

import asyncio
from logging.config import fileConfig

from sqlalchemy import pool
from sqlalchemy.ext.asyncio import async_engine_from_config
from alembic import context

from app.config import settings
from app.models.base import Base
from app.models import user, item  # Import all models

config = context.config
config.set_main_option("sqlalchemy.url", settings.database_url)

if config.config_file_name is not None:
    fileConfig(config.config_file_name)

target_metadata = Base.metadata


def run_migrations_offline() -> None:
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
    )
    with context.begin_transaction():
        context.run_migrations()


def do_run_migrations(connection) -> None:
    context.configure(connection=connection, target_metadata=target_metadata)
    with context.begin_transaction():
        context.run_migrations()


async def run_async_migrations() -> None:
    connectable = async_engine_from_config(
        config.get_section(config.config_ini_section, {}),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )
    async with connectable.connect() as connection:
        await connection.run_sync(do_run_migrations)
    await connectable.dispose()


def run_migrations_online() -> None:
    asyncio.run(run_async_migrations())


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()

Testing

conftest.py

import pytest
from httpx import ASGITransport, AsyncClient
from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession

from app.main import app
from app.database import get_db
from app.models.base import Base


@pytest.fixture
async def db_session():
    engine = create_async_engine(
        "sqlite+aiosqlite:///:memory:",
        echo=True,
    )
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)

    session_maker = async_sessionmaker(engine, expire_on_commit=False)
    async with session_maker() as session:
        yield session

    await engine.dispose()


@pytest.fixture
async def client(db_session: AsyncSession):
    async def override_get_db():
        yield db_session

    app.dependency_overrides[get_db] = override_get_db
    async with AsyncClient(
        transport=ASGITransport(app=app),
        base_url="http://test"
    ) as ac:
        yield ac
    app.dependency_overrides.clear()

Example Test

import pytest
from httpx import AsyncClient


@pytest.mark.asyncio
async def test_create_user(client: AsyncClient):
    response = await client.post(
        "/api/v1/users",
        json={
            "email": "[email protected]",
            "password": "testpassword123",
            "full_name": "Test User",
        },
    )
    assert response.status_code == 201
    data = response.json()
    assert data["email"] == "[email protected]"
    assert "id" in data

Running the Application

# Development
uv run uvicorn app.main:app --reload --host 0.0.0.0 --port 8000

# Production
uv run uvicorn app.main:app --host 0.0.0.0 --port 8000 --workers 4

# Run tests
uv run pytest -v

# Run with coverage
uv run pytest --cov=app --cov-report=html

# Lint and format
uv run ruff check .
uv run ruff format .

# Type check
uv run mypy src/

Best Practices

  • Layered Architecture
  • Routes: Handle HTTP, validation, response formatting
  • Services: Business logic, orchestration
  • Repositories: Data access, queries
  • Dependency Injection
  • Use FastAPI's Depends() for clean DI
  • Inject database sessions, services, configs
  • Type Safety
  • Use Pydantic for all request/response schemas
  • Use SQLAlchemy 2.0 mapped columns with types
  • Enable strict mypy
  • Async First
  • Use async/await throughout
  • Use asyncpg for PostgreSQL
  • Use aiosqlite for testing
  • Configuration
  • Use pydantic-settings for type-safe config
  • Load from environment variables
  • Never commit secrets
  • Testing
  • Use in-memory SQLite for unit tests
  • Use test containers for integration tests
  • Mock external services

How to use it

Copy the folder

Take aiskillstore/python-fastapi from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

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