Your main function needs to be async as well, since the one_time_setup is async. Linking this SO answer that also links to the docs (may come handy!).

https://stackoverflow.com/questions/57399157/runtimewarning-...

Edit: Also tangentially relevant is the article linked by pansa2 in another thread, which was also discussed on HN a few months ago: http://journal.stuffwithstuff.com/2015/02/01/what-color-is-y...