Default executor asyncio

You can also take a look at cpython source (assuming thats what you are using)

My question is, what is the default executor of asyncio?

As of this writing (Feb 2020, Python 3.9 alpha), it's a concurrent.futures.ThreadPoolExecutor with default settings.

Previously one could also call set_default_executor to use a different kind of executor, but as of Python 3.8 it's guaranteed to be a ThreadPoolExecutor. However, its exact settings aren't documented, so they can change in a future Python release. For example, in Python 3.10 it sets the thread_name_prefix property.