How does python import order affect names?
Contrary to what the other answer says, this is a circular import problem. app.__init__ tries to import app.views, which tries to import the app.app Flask created in app.__init__. If the Flask is created before app.__init__ imports app.views, app.views finds app.app. If the Flask is created after the import, it isn't there yet when app.views tries to find it.
Circular imports cause all sorts of horrible problems. It might be difficult, but the best way to handle them is generally to reorganize your code so there aren't circular imports.