Access app_context from another task in Quart

Question

My Quart app is created with a create_app factory method.

I also have a third party library incorporated as an additional task via the create_task method.

I pass a callback function to this library which updates my database (via SQLAlchemy). Unfortunately this does not work and raises the exception:

"Attempt to access app outside of a relevant context"

Pushing the app context does not work:

from quart import current_app as app

async with app.app_context():

Looking at Quarts Context Documentation: https://pgjones.gitlab.io/quart/contexts.html it is obvious why, because the app does not exist in the third party task.

Both of these contexts exist per request and allow the global proxies current_app, request, etc… to be resolved. Note that these contexts are task local, and hence will not exist if a task is spawned by ensure_future or create_task.

Does anyone has any other solution to get the app context from another task?

Edit It still won't work. I am using Quart 0.10.0. A more verbose example of my app looks like this:

from app import create_app

from third_party import ThirdParty

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

@app.before_serving
async def startup():
    async with app.app_context() as app_context:
        await third_party.start()


@app.after_serving
async def shutdown():
    await third_party.stop()


if __name__ == "__main__":
    app.run()

The ThirdParty is basically this:

class ThirdParty:
    async def start(self):
        self.loop.create_task(self.run())

    async def run(self):
        while True:
            await self.wait_for_trigger()
            # executes my callback function
            await self.custom_callback_func()

my callback function is in another module and I pass to the third_party instance:

from quart import current_app as app

async def custom_callback_func():
    async with app.app_context:
        # update_my database
        # raises "Attempt to access app outside of a relevant context"

If the app_context is automatically copied to created tasks from a task with the app context, why is my example not working?

await third_party.start() inside the with app_context statement calls loop.create_task(run()) which runs my assigned callback function. So why is there no app_context inside this callback available?

pgjones · Accepted Answer · 2020-01-20T11:27:45.400

I think you must be using a 0.6.X version of Quart? If so the copy_current_app_context (from quart.ctx) can be used to explicitly copy the context into a new task. For example,

task = asyncio.ensure_future(copy_current_app_context(other_task_function)())

See also this short documentation snippet. Note though that it is written with Quart >= 0.7 which should automatically copy the context between tasks.

Edit: Following an update to the question.

I think you are best placed passing the app instance and using it directly, rather than using current_app in the task. This is because there is no app context after before_serving and before the first request. This may change in Quart though, see this issue.

Thank you very much for your time answering. Could you have another look at my Edit? I am using Quart 0.10.0 and as far as I understand you the app context should be copied to my created task. Thank you for Quart btw :) — Eric, Jan 19 '20 at 22:12

Access app_context from another task in Quart

1 Answers1