asyncio example on "Fluent Python", modified

flags_asyncio.py

#
# c.f. "Fluent Python" (Ja) p577
#
import asyncio
import aiohttp
import sys
import time

POP20_CC = ['CN', 'IN', 'US', 'ID', 'BR', 'PK', 'NG', 'BD', 'RU', 'JP',
            'MX', 'PH', 'VN', 'ET', 'EG', 'DE', 'IR', 'TR', 'CD', 'FR']

BASE_URL = 'http://flupy.org/data/flags'

def show(text):
    print(text, end=' ')
    sys.stdout.flush()

async def get_flag(cc):
    cc_lower = cc.lower()
    url = f'{BASE_URL}/{cc_lower}/{cc_lower}.gif'
    print(url)
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as resp:
            image = await resp.read()
    return image


async def download_one(cc):
    image = await get_flag(cc)
    show(cc)
    with open(f'/tmp/{cc}.gif', 'wb') as f:
        f.write(image)


def download_many(cc_list):
    loop = asyncio.get_event_loop()
    to_do = [download_one(cc) for cc in sorted(cc_list)]
    wait_coro = asyncio.wait(to_do)
    res, _ = loop.run_until_complete(wait_coro)
    loop.close()
    return len(res)

    
def main(download_many):
    t0 = time.time()
    count = download_many(POP20_CC)
    elapsed = time.time() - t0
    print(f'\n{count} flags downloaded in {elapsed:.2f}s')


if __name__ == '__main__':
    main(download_many)