I can easily reproduce this issue with this example:
from threading import Thread
import asyncio
def func():
asyncio.get_event_loop()
Thread(target=func).start()
According to document:
If there is no current event loop set in the current OS thread, the OS thread is main, and set_event_loop() has not yet been called, asyncio will create a new event loop and set it as the current one.
Automatic assignment of a new event loop only happens on the main thread. From the source of asyncio DefaultEventLoopPolicy in events.py
def get_event_loop(self):
"""Get the event loop for the current context.
Returns an instance of EventLoop or raises an exception.
"""
if (self._local._loop is None and
not self._local._set_called and
isinstance(threading.current_thread(), threading._MainThread)):
self.set_event_loop(self.new_event_loop())
if self._local._loop is None:
raise RuntimeError('There is no current event loop in thread %r.'
% threading.current_thread().name)
return self._local._loop
So for a non-main thread, you have to manually set the event loop with asyncio.set_event_loop(asyncio.new_event_loop())
