【六】协程并发
定义tasks时可以设置多个ensure，也可以像多线程那样用append方法实现
tasks = [asyncio.ensure_future(coroutine1),asyncio.ensure_future(coroutine2),asyncio.ensure_future(coroutine3)]for i in range(4, 6):tasks.append(asyncio.ensure_future(do_some_work(i)))
当遇到阻塞时可以使用await让其他协程继续工作
例如：
import asyncioimport timenow = lambda: time.time()async def do_some_work(x):print('Waiting: ', x)await asyncio.sleep(x)return 'Done after {}s'.format(x)coroutine1 = do_some_work(1)coroutine2 = do_some_work(2)coroutine3 = do_some_work(3)tasks = [asyncio.ensure_future(coroutine1),asyncio.ensure_future(coroutine2),asyncio.ensure_future(coroutine3)]for i in range(4, 6):tasks.append(asyncio.ensure_future(do_some_work(i)))loop = asyncio.get_event_loop()start = now()loop.run_until_complete(asyncio.wait(tasks))for task in tasks:print('Task ret: ', task.result())print('TIME: ', now() - start)通过运行时间可以看出aysncio实现了并发。asyncio.wait(tasks) 也可以使用 asyncio.gather(*tasks) ,前者接受一个task列表，后者接收一堆task。
【七】协程嵌套
使用async可以定义协程，协程用于耗时的io操作，我们也可以封装更多的io操作过程，这样就实现了嵌套的协程，即一个协程中await了另外一个协程，如此连接起来。
例如：
import asyncioimport timenow = lambda: time.time()async def do_some_work(x):print('Waiting: ', x)await asyncio.sleep(x)return 'Done after {}s'.format(x)async def main():coroutine1 = do_some_work(1)coroutine2 = do_some_work(2)coroutine3 = do_some_work(4)tasks = [asyncio.ensure_future(coroutine1),asyncio.ensure_future(coroutine2),asyncio.ensure_future(coroutine3)]dones, pendings = await asyncio.wait(tasks)for task in dones:print('Task ret: ', task.result())start = now()loop = asyncio.get_event_loop()loop.run_until_complete(main())print('TIME: ', now() - start)如果使用的是 asyncio.gather创建协程对象，那么await的返回值就是协程运行的结果。
#dones, pendings = await asyncio.wait(tasks)#for task in dones:#print('Task ret: ', task.result())results = await asyncio.gather(*tasks)for result in results:print('Task ret: ', result)不在main协程函数里处理结果，直接返回await的内容，那么最外层的run_until_complete将会返回main协程的结果。
import asyncioimport timenow = lambda: time.time()async def do_some_work(x):print('Waiting: ', x)await asyncio.sleep(x)return 'Done after {}s'.format(x)async def main():coroutine1 = do_some_work(1)coroutine2 = do_some_work(2)coroutine3 = do_some_work(4)tasks = [asyncio.ensure_future(coroutine1),asyncio.ensure_future(coroutine2),asyncio.ensure_future(coroutine3)]return await asyncio.gather(*tasks)start = now()loop = asyncio.get_event_loop()results = loop.run_until_complete(main())for result in results:print('Task ret: ', result)print('TIME: ', now() - start)或者返回使用asyncio.wait方式挂起协程。
import asyncioimport timenow = lambda: time.time()async def do_some_work(x):print('Waiting: ', x)await asyncio.sleep(x)return 'Done after {}s'.format(x)async def main():coroutine1 = do_some_work(1)coroutine2 = do_some_work(2)coroutine3 = do_some_work(4)tasks = [asyncio.ensure_future(coroutine1),asyncio.ensure_future(coroutine2),asyncio.ensure_future(coroutine3)]return await asyncio.wait(tasks)start = now()loop = asyncio.get_event_loop()done, pending = loop.run_until_complete(main())for task in done:print('Task ret: ', task.result())print('TIME: ', now() - start)也可以使用asyncio的as_completed方法
import asyncioimport timenow = lambda: time.time()async def do_some_work(x):print('Waiting: ', x)await asyncio.sleep(x)return 'Done after {}s'.format(x)async def main():coroutine1 = do_some_work(1)coroutine2 = do_some_work(2)coroutine3 = do_some_work(4)tasks = [asyncio.ensure_future(coroutine1),asyncio.ensure_future(coroutine2),asyncio.ensure_future(coroutine3)]for task in asyncio.as_completed(tasks):result = await taskprint('Task ret: {}'.format(result))start = now()loop = asyncio.get_event_loop()done = loop.run_until_complete(main())print('TIME: ', now() - start)由此可见，协程的调用和组合十分的灵活，我们可以发挥想象尽情的浪