On 31 May 2018 at 14:47, Danilo J. S. Bellini <danilo.bell...@gmail.com> wrote:
> The idea is to allow catching exceptions beyond checking their MRO, > using a class that checks the exception instance by implementing > a custom __instancecheck__. > The exception machinery deliberately attempts to avoid instantiating exception objects whenever it can, but that gets significantly more difficult if we always need to create the instance before we can decide whether or not the raised exception matches the given exception handler criteria. So quite aside from any philosophy-of-design questions, we're unlikely to ever implement this simply for laziness-of-evaluation reasons. (There are already lots of circumstances that force instantiation - that doesn't mean we're keen to add more) Cheers, Nick. P.S. There's a somewhat related issue aimed at getting ABCs to work correctly as exception handlers, although that still sticks to the principle that exception handler checks solely consider the exception type, not its value: https://bugs.python.org/issue12029 -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia
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