I think ExceptionSummary could be the visible API, instead of adding an indirection through a separate global function.
Also, I don't think having the "exc_traceback" list of tuples is future-proof. What if we want to add some information to each traceback entry, or refactor it to take __loader__ into account?
Instead, ExceptionSummary could expose the desired operations (e.g. iterate over traceback lines and the associated source code lines) without being constrained by some implementation details.