在python里使用await關(guān)鍵字來等另外一個協(xié)程的實例

更新時間：2020年05月04日 17:59:08 作者：caimouse

這篇文章主要介紹了在python里使用await關(guān)鍵字來等另外一個協(xié)程的實例，具有很好的參考價值，希望對大家有所幫助。一起跟隨小編過來看看吧

一個協(xié)程里可以啟動另外一個協(xié)程，并等待它完成返回結(jié)果，采用await關(guān)鍵字，

例子如下：

import asyncio
 
async def outer():
  print('in outer')
  print('waiting for result1')
  result1 = await phase1()
  print('waiting for result2')
  result2 = await phase2(result1)
  return (result1, result2)
 
async def phase1():
  print('in phase1')
  return 'result1'
 
async def phase2(arg):
  print('in phase2')
  return 'result2 derived from {}'.format(arg)
 
event_loop = asyncio.get_event_loop()
try:
  return_value = event_loop.run_until_complete(outer())
  print('return value: {!r}'.format(return_value))
finally:
  event_loop.close()

輸出結(jié)果如下：
in outer
waiting for result1
in phase1
waiting for result2
in phase2
return value: ('result1', 'result2 derived from result1')

await關(guān)鍵字添加了一個新的協(xié)程到循環(huán)里，而不需要明確地添加協(xié)程到這個事件循環(huán)里。

補充知識：python里使用Condition對象來喚醒指定數(shù)量的協(xié)程

在asyncio庫里，定義Condition對象，它的行為與事件Event有點像，區(qū)別是事件是通知所有對象，Condition對象可以指定一定數(shù)量的協(xié)程被通知，它是通過函數(shù)notify()來實現(xiàn)的，如果參數(shù)里放2，就是通知兩個協(xié)程，例子如下：

import asyncio
 
async def consumer(condition, n):
  with await condition:
    print('consumer {} is waiting'.format(n))
    await condition.wait()
    print('consumer {} triggered'.format(n))
  print('ending consumer {}'.format(n))
 
async def manipulate_condition(condition):
  print('starting manipulate_condition')
 
  # pause to let consumers start
  await asyncio.sleep(0.1)
 
  for i in range(1, 3):
    with await condition:
      print('notifying {} consumers'.format(i))
      condition.notify(n=i)
    await asyncio.sleep(0.1)
 
  with await condition:
    print('notifying remaining consumers')
    condition.notify_all()
 
  print('ending manipulate_condition')
 
async def main(loop):
  # Create a condition
  condition = asyncio.Condition()
 
  # Set up tasks watching the condition
  consumers = [
    consumer(condition, i)
    for i in range(5)
  ]
 
  # Schedule a task to manipulate the condition variable
  loop.create_task(manipulate_condition(condition))
 
  # Wait for the consumers to be done
  await asyncio.wait(consumers)
 
event_loop = asyncio.get_event_loop()
try:
  result = event_loop.run_until_complete(main(event_loop))
finally:
  event_loop.close()

結(jié)果輸出如下：

starting manipulate_condition
consumer 2 is waiting
consumer 3 is waiting
consumer 4 is waiting
consumer 1 is waiting
consumer 0 is waiting
notifying 1 consumers
consumer 2 triggered
ending consumer 2
notifying 2 consumers
consumer 3 triggered
ending consumer 3
consumer 4 triggered
ending consumer 4
notifying remaining consumers
ending manipulate_condition
consumer 1 triggered
ending consumer 1
consumer 0 triggered
ending consumer 0

以上這篇在python里使用await關(guān)鍵字來等另外一個協(xié)程的實例就是小編分享給大家的全部內(nèi)容了，希望能給大家一個參考，也希望大家多多支持腳本之家。

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