async_await.py

"""Download flags of top 20 countries by population
asyncio + aiottp version
Sample run::
    $ python3 flags_asyncio.py
    EG VN IN TR RU ID US DE CN MX JP BD NG ET FR BR PH PK CD IR
    20 flags downloaded in 1.07s
"""
import os
import time
import sys
import asyncio
import aiohttp


POP20_CC = ('CN IN US ID BR PK NG BD RU JP '
            'MX PH VN ET EG DE IR TR CD FR').split()  # <2>

BASE_URL = 'http://flupy.org/data/flags'  # <3>

DEST_DIR = 'downloads/'  # <4>


def save_flag(img, filename):  # <5>
    path = os.path.join(DEST_DIR, filename)
    with open(path, 'wb') as fp:
        fp.write(img)


def show(text):  # <7>
    print(text, end=' ')
    sys.stdout.flush()


async def get_flag(cc):
    url = '{}/{cc}/{cc}.gif'.format(BASE_URL, cc=cc.lower())
    resp = await aiohttp.get(url)
    image = await resp.read()
    return image


async def download_one(cc):
    image = await get_flag(cc)
    show(cc)
    save_flag(image, cc.lower() + '.gif')
    return cc


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):  # <10>
    t0 = time.time()
    count = download_many(POP20_CC)
    elapsed = time.time() - t0
    msg = '\n{} flags downloaded in {:.2f}s'
    print(msg.format(count, elapsed))


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