Python异步上下文 [英] Python asyncio context

问题描述

在线程中，我们有一个称为线程上下文"的东西，在其中我们可以保存一些数据(状态)，以便在特殊线程中进行访问.在异步中，我需要在当前执行路径中保存一些状态，以便所有后续协程都可以访问它.解决办法是什么?注意:我知道每个协程函数都为asyncio中的执行路径实例化，但是由于某些原因，我无法将状态保存在函数属性中.(尽管这种方法仍然不是很好)

In threading, we have something called "Thread Context", in which we can save some data (state) for accessing in a special thread. In asyncio, I need to save some state in current execution path, so that all consequent coroutines can access it. What is the solution? Note: I know each coroutine function is instantiated for an execution path in asyncio, but for some reason I can not save the state in function properties. (Although this method os not very good anyway)

推荐答案

从Python 3.7开始，您可以使用

As of Python 3.7 you can make use of contextvars.ContextVar.

在下面的示例中，我声明了 request_id ，并在 some_outer_coroutine 中设置了值，然后在 some_inner_coroutine 中对其进行了访问.

In the example below I declared request_id and set the value in some_outer_coroutine, then accessed it in some_inner_coroutine.

import asyncio
import contextvars

# declare context var
request_id = contextvars.ContextVar('Id of request.')


async def some_inner_coroutine():
    # get value
    print('Processed inner coroutine of request: {}'.format(request_id.get()))


async def some_outer_coroutine(req_id):
    # set value
    request_id.set(req_id)

    await some_inner_coroutine()

    # get value
    print('Processed outer coroutine of request: {}'.format(request_id.get()))


async def main():
    tasks = []
    for req_id in range(1, 5):
        tasks.append(asyncio.create_task(some_outer_coroutine(req_id)))

    await asyncio.gather(*tasks)


if __name__ == '__main__':
    asyncio.run(main())

输出:

Processed inner coroutine of request: 1
Processed outer coroutine of request: 1
Processed inner coroutine of request: 2
Processed outer coroutine of request: 2
Processed inner coroutine of request: 3
Processed outer coroutine of request: 3
Processed inner coroutine of request: 4
Processed outer coroutine of request: 4

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