What is FastAPI event handlers?

Question

Accepted Answer

**FastAPI** runs **startup and shutdown** handlers for initialization/cleanup.

```python
from fastapi import FastAPI
from contextlib import asynccontextmanager

# Modern approach (FastAPI 0.93+)
@asynccontextmanager
async def lifespan(app: FastAPI):
    # Startup
    print("Starting up...")
    db = await create_db_connection()
    app.state.db = db

yield  # Application runs here

# Shutdown
    print("Shutting down...")
    await db.close()

app = FastAPI(lifespan=lifespan)

@app.get("/items/")
async def get_items():
    db = app.state.db
    return await db.fetch_all("items")

# Legacy approach
app = FastAPI()

@app.on_event("startup")
async def startup():
    print("Starting up...")

@app.on_event("shutdown")
async def shutdown():
    print("Shutting down...")
```

**Common uses:**
- Database connections.
- Redis/cache initialization.
- Background task setup.
- Resource cleanup.

Python: What is FastAPI event handlers?