The except clause is in the "dropbox_auth_finish" view. That might be personal paranoia, but I'm sure that every single timeI think "It's OK to put a `except:` here", it eventually comes back to bite me (without exception ;) )!
I do understand the motivation to keep it minimal (and I think the Flask boilerplate is indeed well understood), but putting together the sample without the Dropbox SDK imports (specifically without an IDE) might end up being a bit more bothersome than optimal : )
Just personal opinion, of course!