asyncio的Semaphore 和 aiohttp 限制并发数量实例

# coding=utf-8
import time
from aiohttp import ClientSession
import asyncio

URL = 'http://httpbin.org/get?a={}'


async def fetch_async (num):
    async with ClientSession() as session:
        async with session.get(URL.format(num)) as response:
            data = await response.json()
            return data['args']['a']


async def print_result (num, semaphore):
    async with semaphore:
        r = await fetch_async(num)
        print(f'fetch({num}) = {r}')


async def main (loop):
    now = time.time()
    semaphore = asyncio.Semaphore(3)
    tasks = [print_result(num, semaphore) for num in range(10)]
    await asyncio.wait(tasks)
    print("总用时", time.time() - now)


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    # -------------------------------------------------------
    try:
        loop.run_until_complete(main(loop))
    finally:
        loop.close()


输出:

fetch(2) = 2
fetch(3) = 3
fetch(4) = 4
fetch(6) = 6
fetch(7) = 7
fetch(9) = 9
fetch(5) = 5
fetch(8) = 8
fetch(1) = 1
fetch(0) = 0
总用时 4.487184286117554

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