Many of the methods in theFlask app object are decorated withsetupmethod, which prevents registering things with the application after it starts running. A similar behavior is inBlueprint, we want to prevent modifying it after registering it at least once. However, the blueprint checking is much less consistent, it's divided up into two parts, is only a warning sometimes, and has a different message. Figure out how we can makeFlask andBlueprint more consistent with this error.