nest-asyncio

Patch asyncio to allow nested event loops

nest-asyncio Permissive license BSD Abandoned ★ 753 v1.6.0 released 2024-01-21

Install

nest-asyncio on PyPI

pip

pip install nest-asyncio

uv

uv add nest-asyncio

poetry

poetry add nest-asyncio

Package facts

License	BSD (permissive)
Python support	supports the current Python release (>=3.5)
Install friction	low — pure-Python wheel
Runtime dependencies	none
Maintenance	abandoned — 935 days since the last release
Last repo commit	2024-01-31 (repository archived)
First released	2018-09-07
Popularity	one of the top 1,000 most-downloaded packages on PyPI (30-day window, as of 2026-08-13)
Known vulnerabilities	none known (OSV.dev, checked 2026-08-13)

Evidence: nest_asyncio-1.6.0-py3-none-any.whl

Keywords: asyncio, nested, eventloop

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 :: 3.5Programming Language :: Python :: 3.6Programming Language :: Python :: 3.7Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9

About nest-asyncio

from the package's own PyPI description — quoted content, verbatim

Introduction

By design asyncio does not allow <https://github.com/python/cpython/issues/66435>_ its event loop to be nested. This presents a practical problem: When in an environment where the event loop is already running it's impossible to run tasks and wait for the result. Trying to do so will give the error "RuntimeError: This event loop is already running".

The issue pops up in various environments, such as web servers, GUI applications and in Jupyter notebooks.

This module patches asyncio to allow nested use of asyncio.run and loop.run_until_complete.

Installation

.. code-block::

pip3 install nest_asyncio

Python 3.5 or higher is required.

Usage

.. code-block:: python

import nest_asyncio
nest_asyncio.apply()

Optionally the specific loop that needs patching can be given as argument to apply, otherwise the current event loop is used. An event loop can be patched whether it is already running or not. Only event loops from asyncio can be patched; Loops from other projects, such as uvloop or quamash, generally can't be patched.

.. |Build| image::...

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AI interpretation — verify before relying

AI-generated interpretation of the package facts above; every digit, version, license, or vulnerability id it cites is grounded in the facts already shown on this page

Patches asyncio to allow nested event loops, enabling asyncio.run() and loop.run_until_complete() to work in environments where an event loop is already running, such as Jupyter notebooks and web servers.

Installation is trivial with no runtime dependencies. However, the package is archived and abandoned as of 2024-01-31, with no maintenance activity for 935 days; it remains marked stable but carries the risk of unfixed issues in future Python versions.

BSD license is permissive and poses no restrictions on use, modification, or distribution in proprietary or open-source projects.

Usage

pip install nest_asyncio==1.6.0

import nest_asyncio
nest_asyncio.apply()

Python 3.5 or higher required; only patches asyncio event loops, not third-party loops like uvloop or quamash.

Verdict: nest_asyncio solves a real problem for running asyncio code in nested contexts with zero dependencies and a permissive license. However, the repository is archived and abandoned since early 2024, leaving no path for maintenance if future Python versions break compatibility or introduce new asyncio internals. Use only if your Python version and asyncio implementation are stable and unlikely to change.

Needs verification

Whether the patch remains compatible with Python 3.13+ and any planned asyncio changes in future releases.
Whether there are known incompatibilities or edge cases with specific web frameworks or Jupyter versions.

nested asyncio event loopsasyncio.run in jupyterevent loop already running fixasync in web frameworksnested event loop patchasyncio jupyter compatibilityrun asyncio inside asyncio