There doesn't appear to be a way to prematurely kill a subprocess using the high-level asyncio subprocess APIs (https://docs.python.org/3.9/library/asyncio-subprocess.html) without getting a traceback on exit.

On exit, the attached program writes the following to stderr:

$ python3.9 kill_subprocess.py

Exception ignored in: <function BaseSubprocessTransport.__del__ at 0x1065f0dc0>
Traceback (most recent call last):
    ...
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed

If I uncomment `# process._transport.close()` or comment `asyncio.sleep(1)`, the walkback disappears. (I get the same behavior in python 3.8. I haven't tried other python versions.)