reloop

Drop-in replacement for nest-asyncio. Allows nested asyncio event loops.

Why reloop?

nest-asyncio has 30M+ downloads/month but was archived in March 2024 after its maintainer passed away. It has known issues with Python 3.12+ (ResourceWarning for unclosed event loops), no way to undo patches, and no support for newer Python internals.

reloop is a maintained, improved replacement:

• revert() support — permanently applying patches is optional; you can undo them
• Context manager — with reloop.applied(): for scoped patching
• Python 3.12+ compatible — no spurious ResourceWarning for unclosed event loops
• Thread-safe — concurrent apply() and revert() calls are safe
• Zero dependencies — just stdlib

Installation

pip install reloop

Quick Start

import reloop

reloop.apply()

That's it. Now asyncio.run() and loop.run_until_complete() work inside running event loops — Jupyter notebooks, LLM libraries, web framework sync handlers, and anywhere else Python's RuntimeError: This event loop is already running gets in your way.

Usage

import asyncio
import reloop

reloop.apply()

async def inner():
    return 42

async def outer():
    # This would normally raise RuntimeError
    return asyncio.run(inner())

asyncio.run(outer())  # works

Scoped Patching

with reloop.applied():
    asyncio.run(outer())  # patched

asyncio.run(outer())  # raises RuntimeError again

Revert

reloop.apply()
# ... use nested loops ...
reloop.revert()  # restore original asyncio behavior

API Reference

reloop.apply() -> None

Patch asyncio to allow nested event loops.

• Idempotent — safe to call multiple times; subsequent calls are no-ops.
• Thread-safe — concurrent calls from multiple threads are safe.

import reloop
reloop.apply()

reloop.revert() -> None

Undo all asyncio patches, restoring original stdlib behavior.

• Idempotent — safe to call multiple times; subsequent calls are no-ops.
• Thread-safe — concurrent calls from multiple threads are safe.

reloop.revert()

reloop.applied() -> contextmanager

Context manager that calls apply() on entry and revert() on exit. Use this when you want nested loop support scoped to a block rather than process-wide.

with reloop.applied():
    asyncio.run(outer())  # nested loops work here

asyncio.run(outer())  # raises RuntimeError again after the block

Migration from nest-asyncio

Search and replace:

- import nest_asyncio
- nest_asyncio.apply()
+ import reloop
+ reloop.apply()

Differences from nest-asyncio

• revert() support — nest-asyncio patches are permanent; reloop can undo them
• Context manager — with reloop.applied(): for scoped patching
• Python 3.12+ fixes — no ResourceWarning for unclosed event loops
• Thread-safe — concurrent apply() calls are safe
• Maintained — nest-asyncio was archived in March 2024

Compatibility

• Python 3.10+
• Zero dependencies

License

MIT