Quickstart Flask application failing for some reason
Seems like a bug: the related issue Werkzeug 0.11 with Flask 0.10.1 and 'app.debug = True' won't start. #798
I create a new virtual environment using python3.5 and meet the same error, but if I don't use the debug mode, it's fine.
And as the issue says, downgrade Werkzeug to 0.10.4 seem works. You can have a try.