I put some detailed comments in the review, but my main large scale concern is with the "traceback.Frame" name. Making "frame object" an ambiguous phrase seems like a bad idea to me, so I've suggested making it "FrameSummary" (or "FrameInfo", but on reflection I prefer the more explicit term). That would then suggest also making it "traceback.StackSummary" for consistency.

I think having the top level API be an iterable would be OK, but may be a little surprising. Is there a major advantage to avoiding building the whole traceback in memory?