The method signature for traceback.format_exc is (limit=None, chain=True). Where limit is an int and chain a bool. See documentation for python2.7 and 3:
Passing an Exception object results in the exception handling code throwing an exception itself and crashing out as a result:
The solution in this case is to simply not pass any arguments to traceback.format_exc. It will automatically fetch the context of the catch block it resides in and gracefully return the traceback as a string, which is what storm.py is expecting.