Python RuntimeError：此事件循环已在运行

Posted 2023-02-16

【中文标题】Python RuntimeError：此事件循环已在运行

【英文标题】：Python RuntimeError: This event loop is already running

【发布时间】：2020-08-22 10:53:03

【问题描述】：

这是一个非常普遍的问题，但我实际上找不到正确的答案。我有以下代码通过 websocket 连接到服务器，我想让它保持活动状态并继续收听它发送的消息，如下所示：

import asyncio
import websockets
import nest_asyncio
nest_asyncio.apply()
            
async def listen_for_message(websocket):
    while True:
        await asyncio.sleep(0)
        message = await websocket.recv()
        print(message)

async def connect_to_dealer():
    websocket = await websockets.connect(websocketadress)

    hello_message = await websocket.recv()
    print(hello_message)

async def my_app():
    websocket = await connect_to_dealer()
    asyncio.ensure_future(listen_for_message(websocket))

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(my_app())
    loop.run_forever()

它会引发错误：

  File "\untitled0.py", line 71, in <module>
    loop.run_forever()
  File "\Anaconda3\lib\asyncio\base_events.py", line 525, in run_forever
    raise RuntimeError('This event loop is already running') 
RuntimeError: This event loop is already running

而且没有

import nest_asyncio
nest_asyncio.apply()

我明白了：

  File "\untitled0.py", line 70, in <module>
    loop.run_until_complete(my_app()) 
  File "\Anaconda3\lib\asyncio\base_events.py", line 570, in run_until_complete
    self.run_forever()
  File "\Anaconda3\lib\asyncio\base_events.py", line 525, in run_forever
    raise RuntimeError('This event loop is already running')
RuntimeError: This event loop is already running

我还是不明白为什么会这样。

【参考方案1】：

loop.run_until_complete() 已经“永远”运行您的循环。

不要将您的 listen_for_message() 作为一个可等待的任务触发，而是等待它。然后永远运行，因为listen_for_message() 本身永远不会返回：

async def my_app():
    websocket = await connect_to_dealer()
    await listen_for_message(websocket)

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(my_app())

请注意，您的 connect_to_dealer() 函数不会返回 websocket；这可能是您想要纠正的疏忽：

async def connect_to_dealer():
    return await websockets.connect(websocketadress)

我删除了那里的hello_message = await websocket.recv() / print(hello_message) 行，因为listen_for_message() 已经收到消息并打印它们。