[Python-Dev] Why do we need Traceback Objects?

[Christian Tismer]

Guido van Rossum wrote:

[me, about embedding tracebacks into frames]

> > Does this make sense? Do I miss something?
> 
> Yes.  It is quite possible to have multiple stack traces lingering
> around that all point to the same stack frames.

Oh, I see. This is a Standard Python specific thing, which I
was about to forget. In my version, this can happen, too,
unless you are in a continuation-protected context already.
There (and that was what I looked at while debugging), this
situation can never happen, since an exception creates
continuation-copies of all the frames while it crawls up.
Since the traceback causes refcount increase, all the frames
protect themselves.

Thank you. I see it is a stackless feature. I can implement it
if I put protection into the core, not just the co-extension.
Frames can carry the tracebacks under the condition that
they are protected (copied) if the traceback fields are
occupied. Great, since this is a rare condition.

Thanks again for the enlightment - chris

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