Startup and Shutdown

The ASGI lifespan specification includes the ability for awaiting coroutines before the first byte is received and after the final byte is sent, through the startup and shutdown lifespan events. This is particularly useful for creating and destroying connection pools. Quart supports this via the decorators before_serving() and after_serving(), which function like before_first_request().

The decorated functions are all called within the app context, allowing current_app and g to be used.

Warning

Use g with caution, as it will reset after all the before_serving functions complete. It can still be used within this context. If you want to create something used in routes, try storing it on the app instead.

To use this functionality simply do the following:

@app.before_serving
async def create_db_pool():
    app.db_pool = await ...
    g.something = something

@app.before_serving
async def use_g():
    g.something.do_something()

@app.route("/")
async def index():
    app.db_pool.execute(...)
    # g.something is not available here

@app.after_serving
async def create_db_pool():
    await app.db_pool.close()

Testing

Quart’s default test client does not wait for the startup and shutdown events. This must be manually added when testing a Quart app using the before_serving or after_serving decorators. A recommended pytest fixture is:

@pytest.fixture(name="app", scope="function")
async def _app():
    app = create_app()  # Initialize app
    await app.startup()
    yield app
    await app.shutdown()

The app fixture can then be used as normal.

@pytest.mark.asyncio
async def test_index(app):
    test_client = app.test_client()
    await test_client.get("/")
    ...