Hi all, A number of people are working on packages that support multiple async backends (e.g., asyncio + trio, or trio + curio, or trio + twisted, ...). So then the question arises... how can I figure out which async library my user is actually using? Answer: install sniffio, and then call sniffio.current_async_library(), and it tells you. Well, right now it only works for trio and asyncio, but if you maintain an async library and you want to make it easier for packages to detect you, then it's easy to add support – see the manual. We considered various clever things, but ultimately decided that the best approach was to use a ContextVar and make it the coroutine runner's responsibility to advertise which async flavor it uses. In particular, this approach works even for hybrid programs that are using multiple coroutine runners in the same loop, like a Twisted program with asyncio-flavored and twisted-flavored coroutines in the same thread, or a Trio program using trio-asyncio to run both asyncio-flavored and trio-flavored coroutines in the same thread. Github: https://github.com/python-trio/sniffio Manual: https://sniffio.readthedocs.io/ PyPI: https://pypi.org/p/sniffio -n -- Nathaniel J. Smith -- https://vorpus.org