nest-asyncio

Patch asyncio to allow nested event loops

Description

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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.


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