parallel async download from https://community.nitrous.io/tutorials/asynchronous-programming-with-python-3

para_async.py

# encoding=utf-8
# para_async.py
import asyncio
import itertools

import aiohttp

@asyncio.coroutine
async def download(url, parts):
    async def get_partial_content(u, i, start, end):
            print(i, start, end)
            async with aiohttp.get(
                u, headers={
                    "Range": "bytes={}-{}".\
                    format(start, end - 1 if end else "")}) as _resp:
                return i, await _resp.read()

    async with aiohttp.head(url) as resp:
            size = int(resp.headers["Content-Length"])

    ranges = list(range(0, size, size // parts))

    res, _ = await asyncio.wait(
        [get_partial_content(url, i, start, end) for i, (start, end) in
         enumerate(itertools.zip_longest(ranges, ranges[1:], fillvalue=""))])

    sorted_result = sorted(task.result() for task in res)
    return b"".join(data for _, data in sorted_result)
        
if __name__ == '__main__':
    image_url = "http://files.vladstudio.com/joy/where_tahrs_live/wall/"\
                "vladstudio_where_tahrs_live_2880x1800_signed.jpg"
    loop = asyncio.get_event_loop()
    bs = loop.run_until_complete(download(image_url, 16))
    
    with open("test_para_async.jpeg", "wb") as fi:
        fi.write(bs)