Why concrete error types are superior to sentinel errors

TL;DR ¶ Exported concrete error types are superior to sentinel errors. They can be more performant, cannot be clobbered, and promote extensibility. Third-party function errutil.Find is a powerful alternative to standard-library function errors.As . Setting the scene ¶ Imagine that you&rsquo;re writing a package named bluesky whose purpose is to check the availability of usernames on Bluesky , the…