Customise the Event Loop

Customising the event loop is often desired in order to use Quart with another library whilst ensuring both use the same loop. The best practice is to create/initialise the third party within the loop created by Quart, by using Startup and Shutdown before_serving functions as so,

@app.before_serving
async def startup():
    loop = asyncio.get_event_loop()
    app.smtp_server = loop.create_server(aiosmtpd.smtp.SMTP, port=1025)
    loop.create_task(app.smtp_server)

@app.after_serving
async def shutdown():
    app.smtp_server.close()

Do not follow this pattern, typically seen in examples, because this creates a new loop separate from the Quart loop for ThirdParty,

loop = asyncio.get_event_loop()
third_party = ThirdParty(loop)
app.run()  # A new loop is created by default

Controlling the event loop

It is the ASGI server running running Quart that owns the event loop that Quart runs within, by default the server is Hypercorn. Both Quart and Hypercorn allow the loop to be specified, the Quart shortcut in development is to pass the loop to the app.run method,

loop = asyncio.get_event_loop()
third_party = ThirdParty(loop)
app.run(loop=loop)

or to use the app.run_task method,

loop = asyncio.get_event_loop()
third_party = ThirdParty(loop)
loop.run_until_complete(app.run_task())

the Hypercorn (production) solution is to utilise the Hypercorn API to do the following,

from hypercorn.asyncio import serve
from hypercorn.config import Config
...
loop = asyncio.get_event_loop()
third_party = ThirdParty(loop)
loop.run_until_complete(serve(app, Config()))
# or even
await serve(app, config)