pep 409 / 415 don't really solve the problem for libraries

test.py

"""pep-409 and pep-415 add support for "raise exception from None" so that
libraries need not expose internal exception cases.

However, this is too broad in scope as it breaks user-land code that would
like to still see the context of where *their* application was handling
the error.

This makes pep-409/415 more or less useless and the problem they'd like
to solve still remains unsolved.

"""

class MyLibrary:
    def get_thing(self):
        try:
            raise KeyError(
                "didn't find some internal thing, nobody should "
                "see this in their logs")
        except KeyError as err:
            raise Exception(
                "Can't do the mylibrary get_thing, "
                "this is the real error, so I raise from None "
                "here, but I realy just want 'err' skipped, not external "
                "context") from None

            # here's what I want - targeted ignore for just the *immediate*
            # exception.  I've tried to hack this together w/o success:

            raise Exception(
                "Can't do the mylibrary get_thing"
            ).replaces(err)


def my_userland_application():
    library = MyLibrary()

    try:
        raise IndexError(
            "some end-user application caught exception that i "
            "really want to see in my logs, but we won't because "
            "MyLibrary is suppressing all exception context")
    except:
        library.get_thing()


# does not show my IndexError
my_userland_application()