nest-asyncio2
Patch asyncio to allow nested event loops
Decision gist · record as of 2026-08-14
Yes, if you need to run async code from within an already-running event loop. The package is lightweight, has no dependencies, and is actively maintained with broad Python version support. The aging maintenance status (182 days since release) is not a concern given the repository is not archived and recent commits exist. No known vulnerabilities. The leaked event loop caveat on Python 3.12+ is minor and documented; use `run_close_loop=True` if it matters for your use case.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.5 or higher.
- Only patches asyncio event loops; loops from other projects like uvloop or quamash cannot be patched.
- Low friction: pure Python wheel with no runtime dependencies.
License · maintenance · safety
BSD (permissive) — BSD license is permissive; you can use this package freely in commercial and private projects with minimal restrictions.
last release 2026-02-13 (182 days) · last repo commit 2026-02-13 · 20 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 41,911,695 downloads/mo, #665 on PyPI
Alternatives
Verify before relying
pip install nest-asyncio2
import nest_asyncio2
nest_asyncio2.apply()
# Now asyncio.run() works even if an event loop is already running
asyncio.run(some_async_function())- Whether the leaked event loop behavior (ResourceWarning on Python 3.12+) will impact your specific use case or environment.
- Compatibility with projects that may already be patched by the original unmaintained nest_asyncio package.
What it is and what it does
nest-asyncio2 solves a fundamental asyncio limitation: by design, Python's asyncio does not allow nested event loops, which causes `RuntimeError: This event loop is already running` when you try to call `asyncio.run()` or `loop.run_until_complete()` from within code that is already executing inside an event loop. This is a practical problem in Jupyter notebooks, web servers, and GUI applications where an event loop is already active.
The package patches asyncio's internals to permit nesting, allowing you to run async code synchronously even when an event loop is already running. It is a fork of the unmaintained original nest_asyncio, with updates for Python 3.12 and 3.14, a `run_close_loop` option to control event loop cleanup, and warnings if conflicting patches are detected. Installation is frictionless (no dependencies), and it supports Python 3.5 through 3.14.
Use it for
- Running async functions from a Jupyter notebook cell without encountering the 'event loop already running' error.
- Calling async code from a synchronous wrapper function in a web framework that already manages an event loop.
- Mixing async and sync code in GUI applications where the event loop is managed by the framework.
- Testing async functions in a test runner that may already have an active event loop.
- Wrapping async libraries (like aiohttp) for use in environments with pre-existing event loops.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you need to run async code from within an already-running event loop.
The package is lightweight, has no dependencies, and is actively maintained with broad Python version support. The aging maintenance status (182 days since release) is not a concern given the repository is not archived and recent commits exist. No known vulnerabilities. The leaked event loop caveat on Python 3.12+ is minor and documented; use `run_close_loop=True` if it matters for your use case.
Install
nest-asyncio2 on PyPI
Before you install
Low friction: pure Python wheel with no runtime dependencies. Maintenance status is aging (182 days since last release), but the repository is active and not archived, with recent commits and explicit support for Python 3.5 through 3.14.
Requires Python 3.5 or higher. Only patches asyncio event loops; loops from other projects like uvloop or quamash cannot be patched.
License in practice
BSD license is permissive; you can use this package freely in commercial and private projects with minimal restrictions.
Quickstart
pip install nest-asyncio2
import nest_asyncio2
nest_asyncio2.apply()
# Now asyncio.run() works even if an event loop is already running
asyncio.run(some_async_function())Verify before relying
- Whether the leaked event loop behavior (ResourceWarning on Python 3.12+) will impact your specific use case or environment.
- Compatibility with projects that may already be patched by the original unmaintained nest_asyncio package.
Package facts
| License | BSD permissive |
| Python support | Supports the current Python release >=3.5 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | None |
| Maintenance | Aging 182 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 41,911,695 / month, #665 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 5 - Production/StableFramework :: AsyncIOIntended Audience :: DevelopersLicense :: OSI Approved :: BSD LicenseProgramming Language :: Python :: 3 :: OnlyProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: 3.5Programming Language :: Python :: 3.6Programming Language :: Python :: 3.7Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9 |
Evidence: nest_asyncio2-1.7.2-py3-none-any.whl
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