python

Python Backend Patterns

Overview

Python patterns for building backend services with FastAPI.

Project Structure

project/
├── app/
│   ├── __init__.py
│   ├── main.py               # FastAPI app
│   ├── config.py             # Configuration
│   ├── dependencies.py       # Dependency injection
│   ├── routers/              # API routes
│   │   ├── __init__.py
│   │   └── users.py
│   ├── services/             # Business logic
│   ├── repositories/         # Data access
│   ├── models/               # SQLAlchemy models
│   ├── schemas/              # Pydantic schemas
│   └── utils/                # Utilities
├── tests/                    # Test files
├── migrations/               # Alembic migrations
├── pyproject.toml
└── requirements.txt

FastAPI Application

Main Application

# app/main.py
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
from contextlib import asynccontextmanager

from app.config import settings
from app.routers import users, auth
from app.database import engine, Base

@asynccontextmanager
async def lifespan(app: FastAPI):
    # Startup
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)
    yield
    # Shutdown
    await engine.dispose()

app = FastAPI(
    title="My API",
    version="1.0.0",
    lifespan=lifespan,
)

app.add_middleware(
    CORSMiddleware,
    allow_origins=settings.cors_origins,
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

app.include_router(auth.router, prefix="/api/auth", tags=["auth"])
app.include_router(users.router, prefix="/api/users", tags=["users"])

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

Configuration

# app/config.py
from pydantic_settings import BaseSettings
from functools import lru_cache

class Settings(BaseSettings):
    database_url: str = "postgresql+asyncpg://localhost/app"
    redis_url: str = "redis://localhost:6379"
    secret_key: str = "your-secret-key"
    access_token_expire_minutes: int = 30
    cors_origins: list[str] = ["http://localhost:3000"]

    class Config:
        env_file = ".env"

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

settings = get_settings()