I vote to close too as it's very hard to fix in a clean way.

A big problem though is that there is a standard for defining exceptions, that also ensures that the exception is pickleable (always call Exception.__init__ with original args), that is not documented (http://docs.python.org/tutorial/errors.html#user-defined-exceptions).

Celery has an elaborate mechanism to rewrite unpickleable exceptions, but it's a massive workaround just to keep the workers running, and shouldn't be part of the stdlib.  It would help if the Python documentation mentioned this though.

Related: http://docs.celeryproject.org/en/latest/userguide/tasks.html#creating-pickleable-exceptions