Since this issue was created, the traceback module changed considerably, and now we have the TracebackException/StackSummary classes which capture information about an exception for later rendering. The lookup_lines arg controls the timing of the file access: if it is false, this is delayed until render-time.

I believe this solves the use case of the logger - the file access can be delayed till the logger thread renders the exception. I'm not sure I understand the event loop use case, but presumably there, too, the exceptions are not being rendered (because we don't want IO during that loop).