Send asynchronous HTTP requests one after another

Question

I am trying to use aiohttp to send requests one after another like this

import aiohttp
import asyncio
from datetime import datetime


async def main():
    request_url = "https://..."
    async with aiohttp.ClientSession() as session:
        while True:
            print(datetime.now())
            async with session.get(request_url) as response:
                json_data = await response.json()
            print(json_data)
            await asyncio.sleep(0.2)


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

So I would expect each datetime print to be 0.2s apart. However, they seem to be about 0.35s apart as I think it takes 0.15s to get the data from the response. Why is this happening? I want it to be asynchronous so it should just go onto the next one?

How can I fix this?

Answer 1

When you use await all next code will wait for end of this code. If you want to run asyncio code asynchronously, you should use functions like asyncio.gather

---

import asyncio
import aiohttp
import datetime


async def fetch(url):
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as response:
            print('#', response.status)


async def worker(queue):
    print('START WORKER')
    while True:
        url = await queue.get()
        await fetch(url)
        queue.task_done()


async def control(queue):
    while True:
        print(datetime.datetime.now())
        queue.put_nowait('https://docs.python.org/')
        await asyncio.sleep(0.2)


async def main():
    queue = asyncio.Queue()
    await asyncio.gather(
        control(queue),
        asyncio.gather(*[worker(queue) for _ in range(10)])
    )


loop = asyncio.get_event_loop()
loop.run_until_complete(main())

Answer 2

Sending http request and fetching response back takes some time. You need excluding this time from asyncio.sleep() call:

import aiohttp
import asyncio
import time
from datetime import datetime


async def main():
    request_url = "https://..."
    async with aiohttp.ClientSession() as session:
        while True:
            print(datetime.now())
            t0 = time.monotonic()
            async with session.get(request_url) as response:
                json_data = await response.json()
            print(json_data)
            t1 = time.monotonic()
            await asyncio.sleep(0.2 - (t1 - t0))


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