Whether you have "as" or not, the value of sys.exc_info() (which is what would be attached as the context to anything you raise in the except block) is the same. So these are not two different cases -- the only difference is whether or not you have a local variable set to sys.exc_info().
On Thu, Mar 4, 2021 at 4:46 PM Baptiste Carvello < devel2...@baptiste-carvello.net> wrote: > Hi, > > I'll take a shoot at this, just to see how it tastes… So, let's say: > > When an exception group reaches a set of traditional "except" clauses, > those are examined one after the other, in the order they are in the > code. That way, exceptions matched by several clauses will cause the > first one to run, same as today. > > A subgroup is built with the subset of exceptions matched by the > examined clause, as the PEP specifies for "except*". If this subgroup is > None, the clause is not selected, and the next clause, if any, is > examined. On the contrary, if the subgroup contains at least one matched > exception, the clause is selected and no other clause will run (again, > same as today). Exceptions not part of the subgroup are discarded. > > The clause body is then run just once (so the boss only gets one email > about KeyboardInterrupt). If the clause uses the "as" form, the "as" > variable is bound to one exception in the subgroup, which one is > unspecified (at least for now). The other ones are discarded, except if > a bare "raise" is reached (below). > > If a bare "raise" is reached while executing the body, the selected > subgroup propagates out of the "try-except" construct. Justification: > the whole group cannot propagate, because today a bare "raise" cannot > reraise exceptions of a type not matched by the clause. However, if a > single-type exception group is handled similar to a single exception in > traditional "except" clauses, it is acceptable to let it propagate. > > So you would have: > > try: > g=BaseExceptionGroup( > [ValueError(), KeyboardInterrupt(), KeyboardInterrupt()]) > raise g > except RuntimeError: # doesn't match > log_the_error() > except KeyboardInterrupt as e: # builds s=g.subgroup(KeyboardInterrupt) > email_the_boss(e) # tells the boss of any one error > raise # reraises s > except BaseException: # would match, but doesn't run > launch_nuclear_attack() > > # BaseExceptionGroup([KeyboardInterrupt(), KeyboardInterrupt()]) > # propagates further, a traditional "except KeyboardInterrupt" > # would catch it. The ValueError is discarded. > > An interesting feature would be: when the matching clause has no "as", > "except" behaves the same as "except*", apart from the fact that only > one clause may run. > > Cheers, > Baptiste > _______________________________________________ > Python-Dev mailing list -- python-dev@python.org > To unsubscribe send an email to python-dev-le...@python.org > https://mail.python.org/mailman3/lists/python-dev.python.org/ > Message archived at > https://mail.python.org/archives/list/python-dev@python.org/message/EXC6BQVHQXUXBHIEWHLSLU6FY7SJKIF3/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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