Django has developing support for asynchronous (“async”) Python, but does not yet support asynchronous views or middleware; they will be coming in a future release.
There is limited support for other parts of the async ecosystem; namely, Django can natively talk ASGI, and some async safety support.
Certain key parts of Django are not able to operate safely in an asynchronous environment, as they have global state that is not coroutine-aware. These parts of Django are classified as “async-unsafe”, and are protected from execution in an asynchronous environment. The ORM is the main example, but there are other parts that are also protected in this way.
If you try to run any of these parts from a thread where there is a running
event loop, you will get a
SynchronousOnlyOperation error. Note that you
don’t have to be inside an async function directly to have this error occur. If
you have called a synchronous function directly from an asynchronous function
without going through something like sync_to_async or a threadpool, then it
can also occur, as your code is still running in an asynchronous context.
If you encounter this error, you should fix your code to not call the offending
code from an async context; instead, write your code that talks to async-unsafe
in its own, synchronous function, and call that using
asgiref.sync.async_to_sync, or any other preferred way of running
synchronous code in its own thread.
If you are absolutely in dire need to run this code from an asynchronous
context - for example, it is being forced on you by an external environment,
and you are sure there is no chance of it being run concurrently (e.g. you are
in a Jupyter notebook), then you can disable the warning with the
DJANGO_ALLOW_ASYNC_UNSAFE environment variable.
Warning
If you enable this option and there is concurrent access to the async-unsafe parts of Django, you may suffer data loss or corruption. Be very careful and do not use this in production environments.
If you need to do this from within Python, do that with os.environ:
os.environ["DJANGO_ALLOW_ASYNC_UNSAFE"] = "true"
Dec 20, 2019