Running two Async Functions where one returns data and another returns Nothing using Asyncio-CodePudding

Lets say I have some tasks I want to run asynchronously.

I want to make a series of 4 API calls asynchronously, but I also would like to have another asynchronous function checking on status of my session.

Using asyncio I have tried:

import aiohttp
import asyncio
async def make_request():
    async with aiohttp.ClientSession() as session:
        async with session.get('http://httpbin.org/get') as resp:
            print(resp.status)
            print(await resp.text())

    return resp

async def say_hello():
    print("Hello")

async def main():

    tasks = []
    for i in range(4):
        tasks.append(asyncio.create_task(make_request()))

    results = await asyncio.gather(*tasks, say_hello(),)
    
if __name__ == "__main__":
    event_loop = asyncio.get_event_loop()
    event_loop.run_until_complete(main())

In reality, my say_hello() is checking a status and updating a class attribute (the session) while making requests according to a set time frequency. How could I accomplish this "status" function running alongside my actual API calls execution in make_request() which return a response object which I later process when finished.

CodePudding user response：

I think you should structure your code a little bit differently. Lets make while True: loop in say_hello() and put await asyncio.sleep(N) there. Move say_hello() out of asyncio.gather:

import aiohttp
import asyncio


async def make_request():
    async with aiohttp.ClientSession() as session:
        async with session.get("http://httpbin.org/get") as resp:
            resp.status
            await resp.text()
            await asyncio.sleep(2)  # sleep here artificially

    return resp


async def say_hello():
    while True:
        # update session here
        # ...
        await asyncio.sleep(1)
        print("Hello")


async def main():

    tasks = []
    for i in range(4):
        tasks.append(asyncio.create_task(make_request()))

    asyncio.create_task(say_hello())

    results = await asyncio.gather(
        *tasks,
    )

    print(results)


if __name__ == "__main__":
    event_loop = asyncio.get_event_loop()
    event_loop.run_until_complete(main())

EDIT: Example with global session:

import aiohttp
import asyncio

session = None
headers = {"MySessionHeader": "0"}

# limit concurrency of connections to 2
sem = asyncio.Semaphore(2)


async def make_request():
    async with sem, session.get(
        "http://httpbin.org/get", headers=headers
    ) as resp:
        resp.status
        print(await resp.text())
        await asyncio.sleep(2)  # sleep here artificially
    return resp


async def update_headers():
    count = 1
    while True:
        await asyncio.sleep(1)
        # update headers of session:
        # eg. update cookies/headers
        headers["MySessionHeader"] = str(count)
        count  = 1


async def main():
    global session
    session = aiohttp.ClientSession()

    tasks = []
    for i in range(24):
        tasks.append(asyncio.create_task(make_request()))

    asyncio.create_task(update_headers())

    results = await asyncio.gather(
        *tasks,
    )

    print(results)

    await session.close()


if __name__ == "__main__":
    event_loop = asyncio.get_event_loop()
    event_loop.run_until_complete(main())