I've tried upgrading from Flask 0.10.1 to 0.12 today and ran into a little issue:
I am maintaining a larger application which also provides a JSON API on top of a subset of it's functionalities via Flask. In order to make error handling consistent I defined a simple mixin class:
class RestExceptionMixin(object):
"""
Mixin for exceptions which can be used in a REST API.
"""
status_code = 400