GeezerVison

This isn't ideal as it makes the exception group's own traceback include the def __exit__(...) frame. For example:

  File "/Volumes/RAMDisk/cpython/Lib/test/test_contextlib.py", line 1220, in test_exception_groups
    with suppress(ValueError):
  File "/Volumes/RAMDisk/cpython/Lib/contextlib.py", line 454, in __exit__
    raise rest from excinst
  File "/Volumes/RAMDisk/cpython/Lib/test/test_contextlib.py", line 1221, in test_exception_groups
    raise eg_all()

in case of the newly added test.

This isn't a big problem because:

• the group's member exceptions contain pristine tracebacks, only the group itself contains extra frames; and
• the raise of the original group is still included in the traceback because we used .split() to create the new object.

Ideally, we wouldn't need this. However, the API of __exit__ makes it impossible to replace the ExceptionGroup instance with another one, while ExceptionGroup itself makes its exceptions read-only.

Was there a specific reason to handle ExceptionGroup but not BaseExceptionGroup?

I doubt it. Want to make a PR?