ExceptionGroup wrapper does not appear to function with except*

[dstufft]

It looks like even on Python 3.11.5, the ExceptionGroup shim is being used, see for instance:

❯ python3.11 -c "import packaging.metadata; print(packaging.metadata.ExceptionGroup.__doc__); print(packaging.metadata.ExceptionGroup); print(__builtins__.ExceptionGroup)"
A minimal implementation of :external:exc:`ExceptionGroup` from Python 3.11.

        If :external:exc:`ExceptionGroup` is already defined by Python itself,
        that version is used instead.

<class 'packaging.metadata.ExceptionGroup'>
<class 'ExceptionGroup'>

This is causing errors not to function correctly with except*.

[dstufft]

Not going to lie, I don't really understand what's happening here.

If I edit packaging/metadata.py and drop a print(type(__builtins__)) it tells me that the type is a dict, but if I do python3.11 -c "print(type(__builtins__))" it tells me the type is a module.

If I change the shim to get activated using:

try:
    ExceptionGroup = ExceptionGroup
except NameError:

    class ExceptionGroup(Exception):  # type: ignore[no-redef]  # noqa: N818
        """A minimal implementation of :external:exc:`ExceptionGroup` from Python 3.11.

        If :external:exc:`ExceptionGroup` is already defined by Python itself,
        that version is used instead.
        """

        message: str
        exceptions: List[Exception]

        def __init__(self, message: str, exceptions: List[Exception]) -> None:
            self.message = message
            self.exceptions = exceptions

        def __repr__(self) -> str:
            return f"{self.__class__.__name__}({self.message!r}, {self.exceptions!r})"

Everything seems to work?

[pradyunsg]

I think the following would be clearer (separating the name lookup vs reassignment as a global) and I'm onboard for moving to a try-except regardless of the specific form.

try:
   ExceptionGroup
except NameError:
   ...
else:
   ExceptionGroup = ExceptionGroup  # all the linter ignores