Python asyncio context

There's also https://github.com/azazel75/metapensiero.asyncio.tasklocal, but you must be aware that tasks are often created internally by libraries and also by asyncio using ensure_future(a_coroutine) and there's no actual way to track these new tasks and initialize their locals (maybe with those of the task that they are created from). (an "hack" whould be setting a loop.set_task_factory() function with something that does the job, hoping that all code uses loop.create_task() to create the tasks, which is not always true...)

Another issue is that if some of your code is executed inside a Future callback Task.current_task() function which is used by both the libraries to select the right copy of locals to serve will always return None...

As of Python 3.7 you can make use of contextvars.ContextVar.

In the example below I declared request_id and set the value in some_outer_coroutine, then accessed it in some_inner_coroutine.

import asyncio
import contextvars

# declare context var
request_id = contextvars.ContextVar('Id of request.')


async def some_inner_coroutine():
    # get value
    print('Processed inner coroutine of request: {}'.format(request_id.get()))


async def some_outer_coroutine(req_id):
    # set value
    request_id.set(req_id)

    await some_inner_coroutine()

    # get value
    print('Processed outer coroutine of request: {}'.format(request_id.get()))


async def main():
    tasks = []
    for req_id in range(1, 5):
        tasks.append(asyncio.create_task(some_outer_coroutine(req_id)))

    await asyncio.gather(*tasks)


if __name__ == '__main__':
    asyncio.run(main())

Output:

Processed inner coroutine of request: 1
Processed outer coroutine of request: 1
Processed inner coroutine of request: 2
Processed outer coroutine of request: 2
Processed inner coroutine of request: 3
Processed outer coroutine of request: 3
Processed inner coroutine of request: 4
Processed outer coroutine of request: 4