# AN-2026-0754: Python 3.14: asyncio.get_event_loop() raises RuntimeError "There is no current event loop in thread 'MainThread'" instead of creating a loop; child watchers removed

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- id: AN-2026-0754 (version 1; cite https://breakwire.org/claim/AN-2026-0754/v/1)
- kind: breaking · status: active · review: editor
- source: <https://docs.python.org/3/whatsnew/3.14.html#:~:text=asyncio.get_event_loop()%20now%20raises%20a%20RuntimeError>
- more sources: <https://github.com/python/cpython/blob/v3.14.10/Lib/asyncio/events.py> <https://github.com/python/cpython/blob/v3.15.2/Objects/moduleobject.c>
- event date: 2025-10-07
- services: python
- affected: engines.python >=3.14
- severity: high
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. What's New in Python 3.14 (opened 2026-11-04) says asyncio.get_event_loop() now raises a RuntimeError if there is no current event loop and no longer implicitly creates one; most uses can be replaced with asyncio.run(), and code that runs blocking work between loop calls can use asyncio.Runner.  [✓0 ✗0]
1. The same page says the deprecated child watcher classes and functions (AbstractChildWatcher, FastChildWatcher, MultiLoopChildWatcher, PidfdChildWatcher, SafeChildWatcher, ThreadedChildWatcher, get_child_watcher(), set_child_watcher()) were removed.  [✓0 ✗0]
2. Lib/asyncio/events.py at v3.14.10 raises RuntimeError('There is no current event loop in thread %r.'). Reproduced 2026-11-04: module-level asyncio.get_event_loop() raises RuntimeError: There is no current event loop in thread 'MainThread'. on CPython 3.14.10 and only emits a DeprecationWarning on 3.13.5. (Earlier versions raised the same RuntimeError in non-main threads.)  [✓0 ✗0]

## Fix
```text
Use asyncio.run(main()) as the entry point; inside coroutines use asyncio.get_running_loop(); for sync code that calls the loop several times use with asyncio.Runner() as r: r.run(...); if you really need a loop object, create it explicitly with loop = asyncio.new_event_loop(); asyncio.set_event_loop(loop). Remove child watcher code (no replacement needed). Upgrade libraries that call get_event_loop() at import time.
```

## Error signatures
- substring: `There is no current event loop in thread` (Lib/asyncio/events.py v3.14.10; reproduced on CPython 3.14.10)
- code: `module 'asyncio' has no attribute 'get_child_watcher'` (CPython message, reproduced 2026-11-04 on CPython 3.14.10)
- code: `module 'asyncio' has no attribute 'set_child_watcher'` (CPython message, reproduced 2026-11-04 on CPython 3.14.10)
- code: `module 'asyncio' has no attribute 'SafeChildWatcher'` (CPython message, reproduced 2026-11-04 on CPython 3.14.10)
- code: `module 'asyncio' has no attribute 'ThreadedChildWatcher'` (CPython message, reproduced 2026-11-04 on CPython 3.14.10)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0754/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28