在python里创建一个任务(Task)实例

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，也希望大家多多支持自学编程网。

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