python async_error ai_generated true

RuntimeError: Event loop is closed

ID: python/runtimeerror-event-loop-closed

Also available as: JSON · Markdown
88%Fix Rate
90%Confidence
120Evidence
2020-01-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
311 active — — —

Root Cause

Occurs when asyncio operations are attempted after the event loop has been closed, commonly during cleanup in aiohttp, asyncpg, or when mixing asyncio.run() with manual loop management.

generic

Workarounds

  1. 92% success Use asyncio.run() as the single entry point and let it manage the loop lifecycle 
    Replace manual loop.run_until_complete() + loop.close() with a single asyncio.run(main()). This properly handles loop creation, running, and cleanup.

    Sources: https://docs.python.org/3/library/asyncio-runner.html

  2. 90% success For aiohttp, use async with for the ClientSession and ensure cleanup before loop closes 
    async with aiohttp.ClientSession() as session:
    async with session.get(url) as resp:
        return await resp.json()
# Session is properly closed before the event loop shuts down

    Sources: https://docs.aiohttp.org/en/stable/client_quickstart.html

  3. 85% success On Windows, set WindowsSelectorEventLoopPolicy to avoid ProactorEventLoop close issues 
    import asyncio
import sys
if sys.platform == 'win32':
    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

    Sources: https://docs.python.org/3/library/asyncio-platforms.html

Dead Ends

Common approaches that don't work:

  1. Calling asyncio.get_event_loop() to get a new loop after it was closed 90% fail

    get_event_loop() returns the already-closed loop in Python 3.10+. It does not create a new one. The returned loop raises RuntimeError on any operation.

  2. Wrapping everything in try/except to suppress the error 75% fail

    Suppressing the error masks resource leaks. Connections, file handles, and background tasks won't be cleaned up properly, causing data corruption or resource exhaustion.

Error Chain

Preceded by:
Frequently confused with: