Description

AsyncRunner fails to instantiate on Python 3.14 with a RuntimeError because asyncio.get_event_loop() now raises an error when no event loop is running.

Reproduction

from adaptive import Learner1D
from adaptive.runner import AsyncRunner

def f(x):
    return x

learner = Learner1D(f, (-1, 1))
runner = AsyncRunner(learner, npoints_goal=10)

Error on Python 3.14:

RuntimeError: There is no current event loop in thread 'MainThread'.

Cause

In adaptive/runner.py line 629:

self.ioloop = ioloop or asyncio.get_event_loop()

The behavior of asyncio.get_event_loop() changed across Python versions:

• Python 3.10: Deprecated when no running event loop exists
• Python 3.12: Emits DeprecationWarning
• Python 3.14: Raises RuntimeError

Proposed Fix

Replace with a version-agnostic approach:

if ioloop is not None:
    self.ioloop = ioloop
else:
    try:
        self.ioloop = asyncio.get_running_loop()
    except RuntimeError:
        self.ioloop = asyncio.new_event_loop()
        asyncio.set_event_loop(self.ioloop)

This works on Python 3.7+ and handles all cases correctly.