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在python里创建一个任务(Task)实例

apacheer 2020-04-26 07:05 40 查看 https://www.geek-share.com/det

与事件循环进行交互,最基本的方式就是任务,任务封装了协程和自动跟踪它的状态。任务是Future类的子类,所以其它协程可以等待任务完成,或当这些任务完成获取返回结果。

在这里通过create_task()函数来创建一个任务实例,然后事件循环就运行这个任务,直到这个任务返回为止:

import asyncio

async def task_func():
print('in task_func')
return 'the result'

async def main(loop):
print('creating task')
task = loop.create_task(task_func())
print('waiting for {!r}'.format(task))
return_value = await task
print('task completed {!r}'.format(task))
print('return value: {!r}'.format(return_value))

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

结果输出如下:

creating task
waiting for <Task pending coro=<task_func() running at D:\work\csdn\python_Game1\example\asyncio_create_task.py:4>>
in task_func
task completed <Task finished coro=<task_func() done, defined at D:\work\csdn\python_Game1\example\asyncio_create_task.py:4> result='the result'>
return value: 'the result'

补充知识:python里创建任务执行一半时取消任务执行

下例子来演示创建任务执行一半时取消任务执行,这时会抛出异常CancelledError,同时也提供了一个机会来删除占用资源等等:

import asyncio

async def task_func():
print('in task_func, sleeping')
try:
await asyncio.sleep(1)
except asyncio.CancelledError:
print('task_func was canceled')
raise
return 'the result'

def task_canceller(t):
print('in task_canceller')
t.cancel()
print('canceled the task')

async def main(loop):
print('creating task')
task = loop.create_task(task_func())
loop.call_soon(task_canceller, task)
try:
await task
except asyncio.CancelledError:
print('main() also sees task as canceled')

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

结果输出如下:

creating task
in task_func, sleeping
in task_canceller
canceled the task
task_func was canceled
main() also sees task as canceled

以上这篇在python里创建一个任务(Task)实例就是小编分享给大家的全部内容了,希望能给大家一个参考

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