[Python-Dev] Asynchronous use of Traceback objects (original) (raw)

Michael Hudson mwh at python.net
Sun Sep 4 12:39:38 CEST 2005

Christopher Armstrong <radeex at gmail.com> writes:

I had the idea to create a fake Traceback object in Python that doesn't hold references to any frame objects, but is still able to be passed to 'raise' and formatted as tracebacks are, etc. Unfortunately, raise does a type check on its third argument and, besides, it seems the traceback formatting functions are very reliant on the internal structure of traceback objects, so that didn't work.

An option you may not have considered is to ditch the C code that formats tracebacks and always use traceback.py (this has a few obvious problems -- what do you do if traceback.py fails to import, what if formatting the traceback raises an error -- but nothing too horrendous, I think).

Less duplication and less C code are always good things (IMHO, at least).

It does seem that I would be able to construct a passable fake Traceback object from C code -- one that had references to fake frames. These fake objects would only remember the original line numbers, filenames and so forth so that traceback printing could still work. I can try implementing this soon, but I'd just like to make sure I'm on the right track. For example, perhaps a better idea would be to change the traceback-printing functions to use Python attribute lookup instead of internal structure lookup,

My suggestion above would obviously acheive this bit :)

and then change raise to accept arbitrary Python objects as its third argument, as long as it matches the traceback interface. That would probably mean much more work, though.

One concern is that I really don't like requiring C modules to use Twisted; all of the ones currently in there are optional.

Well, presumably this is optional too -- you only need it if you want informative tracebacks...

What's the likelihood of such a traceback-constructor getting its way into CPython if I do implement it?

I'd support more flexibility in this area. I'm not sure what the best approach is, though.

Cheers, mwh

-- I have both hands clapping, but I'm still not sure it's a sound. When I tried deciding if it were a sound while clapping only one hand, I fell off my chair. -- Peter Hansen, Zen master, comp.lang.python

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