Shold not retry asyncio.CancelledError

[KKomarov]

We should not retry CanceledError exceptions because it can lead to a severe bug when canceled coroutine will continue running in the background because retry stops it to cancel.

"suppressing cancellation completely is not common and is actively discouraged" cancel()

Here is the test. Should raise concurrent.futures._base.CancelledError after 1 second. Instead, it raises tenacity.RetryError after 5 seconds

import tenacity
import asyncio


async def test_retry_cancelled():
	@tenacity.retry(stop=tenacity.stop_after_delay(5))
	async def some_work():
		print('starting work')
		await asyncio.sleep(1)
		await asyncio.sleep(1)
		raise Exception('wow!')

	fut = asyncio.ensure_future(some_work())
	await asyncio.sleep(1)
	fut.cancel()
	await fut


asyncio.get_event_loop().run_until_complete(test_retry_cancelled())

[achimnol]

Since Python 3.8, asyncio.CancelledError became a BaseException (not Exception), your example works as expected in Python 3.8 (raising cancellation error after 1 second). Though, we need to add a separate CancelledError handling for Python 3.7 or older.