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Sarj Sarj Sarj Standards

no-fastapi-on-event

Deprecated FastAPI or Starlette on_event lifecycle registration.

SARJ427 Rule source Tests Catalog JSON

Why

The on_event API is deprecated and splits related startup and shutdown state across callbacks; lifespan keeps acquisition and cleanup in one async context manager and is the supported lifecycle contract.

Fix

Define an async lifespan context manager and pass it as FastAPI(lifespan=...) or Starlette(lifespan=...).

Examples

Before — flagged Do not register startup through on_event
app/main.py
from fastapi import FastAPI


app = FastAPI()




@app.on_event("startup")
async def start() -> None:
    pass
After — preferred Pair startup and shutdown in lifespan
app/main.py
from contextlib import asynccontextmanager
from fastapi import FastAPI




@asynccontextmanager
async def lifespan(app: FastAPI):
    yield




app = FastAPI(lifespan=lifespan)