Proposal changed from "err, tb" to "err with tb" at Brett's good suggestion.
The rest of this message is a bit of a sidetrack; skimmers can stop now. Nick Maclaren wrote: >"Jim Jewett" <jimjjewett at gmail.com> wrote: >> Guido van Rossum wrote: >> > [multiple threads => don't share] whatever object >> > contains the head of the chain of tracebacks >> So (full) exceptions can't be unitary objects. As Shane pointed out[1], the *traceback* could be a unitary object holding all three pieces of information. The problem is that we don't want every except clause adding boilerplate to get the exception back out. [1] http://mail.python.org/pipermail/python-dev/2007-February/071417.html >> In theory, raising an already-instantiated instance could indicate "no >> traceback", which could make pre-cooked exceptions even lighter. > The instance contains all of the information about the details, such > as the exact operation, the values and the context (including the > traceback). ... > ... the action of turning an instance into an object disables > the ability to fix up the exception and continue. ... > I don't know of any in the Unix or Microsoft environments, but > there may be a few in specialised areas. Lisp does it. The cost is that instead of dying, those frames become a continuation, and you need to keep around lots of extra (probable) garbage. Dealing with this cleanly was (once upon a time) one of the advantages of Stackless Python. Unfortunately, extension modules can call back into python from the middle of a C function, so the clean restarting was largely limited to pure python frames; trying to get as close as possible for other code made the implementation fairly complicated. > Harking back to your point, your "already-instantiated instance" > is actually an object derived directly from the exception class, and > everything becomes clear. Because it is an object, any context it > includes was a snapshot and is no longer valid. In your case, you > would want it to have "context: unknown". Rather, I want "context: irrelevant" so it won't bother to keep the context alive. That is clearly the right thing for a normal StopIteration. It isn't the right thing for all pre-instantiated exceptions. Whether it is the right thing often enough to ask those others to use the typical idiom -- maybe. -jJ _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
