Define a startup and shutdown logic

[data-corentinv]

Define a startup and shutdown logic using the lifespan parameter of the FastAPI app, and a "context manager" (I'll show you what that is in a second).

Let's start with an example and then see it in detail.

We create an async function lifespan() with yield like this:

from contextlib import asynccontextmanager
from fastapi import FastAPI

def fake_answer_to_everything_ml_model(x: float):
    return x * 42

ml_models = {}

@asynccontextmanager
async def lifespan(app: FastAPI):
    # Load the ML model
    ml_models["answer_to_everything"] = fake_answer_to_everything_ml_model
    yield
    # Clean up the ML models and release the resources
    ml_models.clear()

app = FastAPI(lifespan=lifespan)

@app.get("/predict")
async def predict(x: float):
    result = ml_models["answer_to_everything"](x)
    return {"result": result}

Source: https://fastapi.tiangolo.com/advanced/events/