带有异步def的python asyncio add_done_callback [英] python asyncio add_done_callback with async def

问题描述

我有2个函数:第一个函数def_a是异步函数，第二个函数def_b是常规函数，并以def_a的结果作为add_done_callback的回调进行调用功能.

I have 2 functions: The first one, def_a, is an asynchronous function and the second one is def_b which is a regular function and called with the result of def_a as a callback with the add_done_callback function.

我的代码如下:

import asyncio

def def_b(result):
    next_number = result.result()
    # some work on the next_number
    print(next_number + 1)

async def def_a(number):
    await some_async_work(number)
    return number + 1

loop = asyncio.get_event_loop()
task = asyncio.ensure_future(def_a(1))
task.add_done_callback(def_b)
response = loop.run_until_complete(task)
loop.close()

它工作得很好.

当第二个功能def_b也变得异步时，问题开始了.现在看起来像这样:

The problem began when also the second function, def_b, became asynchronous. Now it looks like this:

async def def_b(result):
    next_number = result.result()
    # some asynchronous work on the next_number
    print(next_number + 1)

但是现在我不能将其提供给add_done_callback函数，因为它不是常规函数.

But now I can not provide it to the add_done_callback function, because it's not a regular function.

我的问题是-如果def_b是异步的，是否可以以及如何向add_done_callback函数提供def_b?

My question is- Is it possible and how can I provide def_b to the add_done_callback function if def_b is asynchronous?

推荐答案

add_done_callback被认为是低级"接口.使用协同程序时，您可以将其链接在许多方面，例如:

add_done_callback is considered a "low level" interface. When working with coroutines, you can chain them in many ways, for example:

import asyncio


async def my_callback(result):
    print("my_callback got:", result)
    return "My return value is ignored"


async def coro(number):
    await asyncio.sleep(number)
    return number + 1


async def add_success_callback(fut, callback):
    result = await fut
    await callback(result)
    return result


loop = asyncio.get_event_loop()
task = asyncio.ensure_future(coro(1))
task = add_success_callback(task, my_callback)
response = loop.run_until_complete(task)
print("response:", response)
loop.close()

请记住，如果您的未来引发异常，add_done_callback仍会调用回调(但调用result.result()会引发异常).

Keep in mind add_done_callback will still call the callback if your future raises an exception (but calling result.result() will raise it).

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