The package-based application structure that we just explored may be suitable for a large number of applications. However, Flask offers us a level of abstraction née Blueprints, which formalizes and enforces a separation of concerns at the level of views.
Note
Do not confuse the concept of a blueprint in Flask, which is an abstraction to factor an application into more discrete components, with that of the Packt book series by the same name!
A Flask application that has become too unwieldy can be factored into a set of discrete blueprints—each with their own mapping of URIs and view functions, static resources (for example, JavaScript and CSS files), Jinja templates, and even Flask extensions. In many respects, blueprints are very similar to the Flask applications themselves. However, a blueprint is not an independent Flask application and cannot be run independently as an application itself, as described in the official Flask documentation:
A blueprint in Flask is...