On Sun, Feb 28, 2021 at 2:40 AM Irit Katriel <iritkatr...@googlemail.com> wrote:
> > In earlier versions of the PEP ExceptionGroup was not immutable and split > actually removed matching exceptions from it. > It was also iterable so you could get a flat list of all the contained > leaf exceptions. Then we changed it. > > ExceptionGroup is a tree of exceptions, and the internal nodes of the tree > (which are ExceptionGroups) have metadata on them - context, cause, > traceback. > If you want the full traceback of a leaf exception you need to concatenate > the tracebacks of all the exceptions on the path from the root to the leaf. > If you flatten an ExceptionGroup and create a new list > ExceptionGroup(list(eg)) you don't lose metadata (unless eg's tree has > depth 1). > Is this a typo? Did you mean "If you flatten [it] and create a new list... you *do* lose metadata (unless ... depth 1)"? > Similarly, if you add an exception it needs to have matching metadata to > the ExceptionGroup you are adding it to. It's too easy to get that wrong. > > split() and subgroup() take care to preserve the correct metadata on all > the internal nodes, and if you just use them you only make safe operations. > This is why I am hesitating to add iteration utilities to the API. Like we > did, people will naturally try that first, and it's not the safest API. > > We actually have the OSErrors example in the PEP, just above > https://www.python.org/dev/peps/pep-0654/#caught-exception-objects: > > try: > low_level_os_operation() > except *OSerror as errors: > raise errors.subgroup(lambda e: e.errno != errno.EPIPE) from None > > > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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