[issue3112] implement PEP 3134 exception reporting

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

Le dimanche 22 juin 2008 à 20:40 +0000, Adam Olsen a écrit :
> > How do you duplicate an instance of an user-defined exception? Using
> an
> > equivalent of copy.deepcopy()? It will probably end up much more
> > expensive than the above-mentioned O(n) search.
> 
> Passing in e.args is probably sufficient.

I think it's very optimistic :-) Some exception objects can hold dynamic
state which is simply not stored in the "args" tuple. See Twisted's
Failure objects for an extreme example:
http://twistedmatrix.com/trac/browser/trunk/twisted/python/failure.py

(yes, it is used an an exception: see "raise self" in the trap() method)

> Can be, or will be?  Only the most common behaviour needs to be optimized.

Well, the "most common behaviour" is a very short context chain, which
is already optimized by my reference-avoidance proposal...

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