{:ok, x} | {:err, y} is my favorite pattern. You can make sure that the caller handles both cases, the ok case and the error case. What you put in y is up to you. If you have dependencies you can decide the bubble up error or return something that you want. We have a bigger system in Elixir and it was trivial to write the correct implementation for exponential backoff to interact with the outside word (calling lots of external services that sometimes time out). With Python this is not as trivial because Guido hates pattern matching and you have catch exceptions and do if else a lot. With Elixir I see immediately while developing if I left out a case. With Python I see it in production when we crashed.