为什么wait不等待asyncio。创建\u subprocess\u exec()

我正在编写一个基于教程的协同程序,以在python中执行shell命令。以下是基本信息:

import asyncio

async def async_procedure():
    process = await asyncio.create_subprocess_exec('ping', '-c', '2', 'google.com')
    await process.wait()
    print('async procedure done.')

loop = asyncio.get_event_loop()
loop.run_until_complete(async_procedure())
loop.close()

上面的代码工作得很好。结果如下:

PING google.com (...) 56(84) bytes of data.
64 bytes from ...: icmp_seq=1 ttl=46 time=34.8 ms
64 bytes from ...: icmp_seq=2 ttl=46 time=34.5 ms

--- google.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 33.771/34.437/34.881/0.407 ms
Process done!

当我尝试删除进程时。等待():

async def async_procedure():
    await asyncio.create_subprocess_exec('ping', '-c', '2', 'google.com')
    print('async procedure done.')

脚本无法按预期工作:

Process done! # This line should be lastest line
PING google.com (...) 56(84) bytes of data.
64 bytes from ...: icmp_seq=1 ttl=46 time=21.1 ms
64 bytes from ...: icmp_seq=2 ttl=46 time=21.8 ms

--- google.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 21.135/21.469/21.803/0.334 ms

但在一个非常相似的例子中没有问题:

async def async_procedure():
    await asyncio.sleep(2)
    print('async procedure done')

• 那么为什么wait不等待asyncio呢。创建_subprocess_exec()?

文档( https://docs.python.org/3/library/asyncio-task.html#coroutine )表示:

结果=等待未来或结果=未来收益 暂停 在未来完成之前,协同路由将返回未来结果,或引发异常,该异常将被传播。(如果取消future,将引发CancelledError异常。)请注意,任务是未来,关于未来的所有说法也适用于任务。

结果=等待协同方案或结果=协同方案的收益 等待 让另一个协同例程生成结果(或引发异常,异常将被传播)。协同路由表达式必须是对另一个协同路由的调用。

返回表达式使用wait或yield from向正在等待此结果的协同例程生成结果。

raise exception–使用wait或yield from在等待此异常的协同程序中引发异常。

• 协同路由时,流程的实际流程是什么 正在挂起 和 等待 ?

下面是asyncio的源代码。创建\u subprocess\u exec()和asyncio。sleep()是协同程序。它们都是协同程序:

@coroutine
def create_subprocess_exec(program, *args, stdin=None, stdout=None,
                           stderr=None, loop=None,
                           limit=streams._DEFAULT_LIMIT, **kwds):
    if loop is None:
        loop = events.get_event_loop()
    protocol_factory = lambda: SubprocessStreamProtocol(limit=limit,
                                                        loop=loop)
    transport, protocol = yield from loop.subprocess_exec(
                                            protocol_factory,
                                            program, *args,
                                            stdin=stdin, stdout=stdout,
                                            stderr=stderr, **kwds)
    return Process(transport, protocol, loop)


@coroutine
def sleep(delay, result=None, *, loop=None):
    """Coroutine that completes after a given time (in seconds)."""
    if delay == 0:
        yield
        return result

    if loop is None:
        loop = events.get_event_loop()
    future = loop.create_future()
    h = future._loop.call_later(delay,
                                futures._set_result_unless_cancelled,
                                future, result)
    try:
        return (yield from future)
    finally:
        h.cancel()