Well, I'd say that if tracing is enabled and is disabled automatically by Python (thus breaking a working debugger which would usually be used to diagnose the error), I'd at least consider issuing some warning to stderr... (probably warnings.warn cannot be used directly as the stack is at its max depth, but a choice could be raising the max depth, using warnings.warn and then restoring the max depth value in a try..finally -- or at least printing something to stderr regardless of warnings.warn).

I.e.: as this is a rare situation and should only happen when you're debugging, I think printing something to stderr regarding that is definitely worth it regardless of chained exceptions (on many cases I had to help users instrument a simple tracer just to detect where it was disabled -- yes, on some of those they were catching all exceptions on some block -- so, program which worked with the recursion stopped having a working debugger).