[FIXED] Ensuring future of recursive function in aiohttp/asyncio

Issue

I'm having an issue with a recursive function not properly being called within an event loop. I have the following:

async def get_response(session, url, attempt=0):
    async with session.get(url) as response:
        if response.status == 200:
            return await response.json()
        elif attempt < 3:
            # This never gets called, a coroutine is returned
            return get_response(session, url, attempt + 1)
        else:
            return None

async def main(loop):
    output = []
    urls = ["https://httpbin.org/json"]
    async with aiohttp.ClientSession(loop=loop) as session:
        tasks = []
        for url in urls:
            tasks.append(asyncio.ensure_future(get_response(session, url)))
        for future in await asyncio.gather(*tasks):
            output.append(future)
    return output

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    output = loop.run_until_complete(main(loop))

The problem arises in get_response where if attempt < 3 it won't actually run the function again. The above code will work just fine since https://httpbin.org/json will return a 200 code. Correct me if I'm wrong (because I probably am) but I'm thinking that since that iteration of the function isn't in the list of tasks in main then it won't actually run? What I get in return when I debug is an actual coroutine object rather than None as I had intended.

What is the proper way to ensure a recursive function within a future will be called again if necessary?

Solution

As get_response is async, you need to await it when calling it, even when doing so from itself. So, you need to change:

            return get_response(session, url, attempt + 1)

to:

            return await get_response(session, url, attempt + 1)

Answered By - user4815162342