python/cpython · error · RuntimeError

Runner.run() cannot be called from a running event loop

Error message

Runner.run() cannot be called from a running event loop

What it means

Error "Runner.run() cannot be called from a running event loop" thrown in python/cpython.

Source

Thrown at Lib/asyncio/runners.py:92

            loop.run_until_complete(
                loop.shutdown_default_executor(constants.THREAD_JOIN_TIMEOUT))
        finally:
            if self._set_event_loop:
                events.set_event_loop(None)
            loop.close()
            self._loop = None
            self._state = _State.CLOSED

    def get_loop(self):
        """Return embedded event loop."""
        self._lazy_init()
        return self._loop

    def run(self, coro, *, context=None):
        """Run code in the embedded event loop."""
        if events._get_running_loop() is not None:
            # fail fast with short traceback
            raise RuntimeError(
                "Runner.run() cannot be called from a running event loop")

        self._lazy_init()

        if not coroutines.iscoroutine(coro):
            if inspect.isawaitable(coro):
                async def _wrap_awaitable(awaitable):
                    return await awaitable

                coro = _wrap_awaitable(coro)
            else:
                raise TypeError('An asyncio.Future, a coroutine or an '
                                'awaitable is required')

        if context is None:
            context = self._context

        task = self._loop.create_task(coro, context=context)

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Do not call Runner.run() from inside a running event loop; await the coroutine directly instead.
2. Call Runner.run() only from synchronous top-level code.

When it happens

Trigger: Raised when Runner.run() is called from within an already-running event loop.

Common situations: See trigger scenarios.

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/b4fffbd5e2062ba1. Report an issue: GitHub.