[Python-Dev] Traceback problem (original) (raw)

Christian Tismer tismer@tismer.com
Wed, 26 Feb 2003 03:40:11 +0100

Guido van Rossum wrote:

p.s.: I would probably have done the exception saving in the caller's frame, where it belongs, IMHO.

I'm going to see if this is feasible. The current method is almost certainly more efficient, but seems very backwards.

Watch out though. There are situations where an exception needs to be stored but no frame is available (when executing purely in C). There is always a thread state.

I've been sitting a while over this puzzle now.

tstate has two different kinds of exceptions: There are tstate->exc_XXX and tstate->curexc_XXX.

I have been searching through the whole source trunk to validate my thought:

All internal stuff is only concerned with handling tstate->curexc_XXX. The tstate->exc_XXX is only used in ceval.c .

References to tstate->exc_XXX are only in pystate.c (clearing stuff) and sysmodule.c (accessing stuff). The only place where tstate->exc_XXX is filled with life is ceval.c, which indicates that this is purely interpreter- -related and has nothing to do with the internal exception state. It is eval_frame which checks for exceptions, normalizes them and turns them into interpreter-level exceptions, around line 2360 of ceval.c .

After stating that, I conclude that tstate.exc_XXX can only be in use if there is an existing interpreter with an existing frame. Nobody else makes use of this structure. So, whenever you have to save this, you can expect a valid frame waiting in f_back that will be able to take it.

(This all under the maybe false assumption that I'm not wrong).

Still not proposing a change. But thanks for the time, I understood quite a lot more of the internals, now.

all the best -- chris

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