>> As a note, the original request was for a Python-level tracing function (so that in the future other Python implementations also provide that function) -- does this need a PEP?

> What do you mean by a Python-level tracing function?

I mean that it's a function to be called from Python (not only from C) -- which hopefully could be adopted by other Python implementations in the long run. 

I.e.: something as adding a thread_id to sys.settrace -- sys.settrace(trace_func, thread_id=None).