python里怎么实现多个协程一起执行，只要完成一个就返回一个协程

需要使用新的函数as_completed()来实现，可以把多个并发的协程一起给它，但它把返回的结果变成一个生成器，每次返回一个协程的结果，与函数wait()一样，执行协程是乱序的，不会等所有协程执行完成才返回。例子：

import asyncio


async def phase(i):
    print('in phase {}'.format(i))
    await asyncio.sleep(0.5 - (0.1 * i))
    print('done with phase {}'.format(i))
    return 'phase {} result'.format(i)


async def main(num_phases):
    print('starting main')
    phases = [
        phase(i)
        for i in range(num_phases)
    ]
    print('waiting for phases to complete')
    results = []
    for next_to_complete in asyncio.as_completed(phases):
        answer = await next_to_complete
        print('received answer {!r}'.format(answer))
        results.append(answer)
    print('results: {!r}'.format(results))
    return results


event_loop = asyncio.get_event_loop()
try:
    event_loop.run_until_complete(main(3))
finally:
    event_loop.close()

结果输出如下：

starting main
waiting for phases to complete
in phase 2
in phase 1
in phase 0
done with phase 2
received answer 'phase 2 result'
done with phase 1
received answer 'phase 1 result'
done with phase 0
received answer 'phase 0 result'
results: ['phase 2 result', 'phase 1 result', 'phase 0 result']