Treat `KeyboardInterrupt` or `SystemExit` the same on program exit even if they are inside exception groups

Feature or enhancement

Proposal:

A KeyboardInterrupt or SystemExit inside a BaseExceptionGroup should be treated like a bare KeyboardInterrupt or SystemExit.

PS C:\...> python x.py
  + Exception Group Traceback (most recent call last):
  |   File "C:\...\x.py", line 1, in <module>
  |     raise BaseExceptionGroup("ki in an exception group", [KeyboardInterrupt()])
  | BaseExceptionGroup: ki in an exception group (1 sub-exception)
  +-+---------------- 1 ----------------
    | KeyboardInterrupt
    +------------------------------------
PS C:\...> $LastExitCode
1


PS C:\...> python x.py
Traceback (most recent call last):
  File "C:\...\x.py", line 1, in <module>
    raise KeyboardInterrupt()
KeyboardInterrupt
PS C:\...> $LastExitCode
-1073741510

Looking at the CPython source code, I believe _Py_HandleSystemExitAndKeyboardInterrupt is the relevant function.

Points for it:

• less pitfalls for a 3rd party using exception groups
• see any other failures (as exceptions) upon shutdown (ATM the workaround requires discarding the other exceptions)

Points against:

• SystemExit in an exception group prints out the stack trace, unlike when it's not in an exception group
  • we could make them consistent (filter out SystemExit and print the exception group then)

I volunteer to implement this if this is fine.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

EDIT: I have now made a post. See https://discuss.python.org/t/keyboardinterrupt-and-systemexit-in-exception-groups-should-be-considered-for-pythons-exit-code/82816

Links to previous discussion of this feature:

I have tried some basic keyword searches as well as some digging in blame, but I can't find any previous discussion.

Start with CPython's _Py_HandleSystemExitAndKeyboardInterrupt, which the issue identifies as the relevant entry point, and reproduce the two exit-code examples using a script that raises a bare exception and one inside a BaseExceptionGroup. Read the linked discussion before deciding how SystemExit output should be handled; done means grouped KeyboardInterrupt and SystemExit follow the intended standalone exit behavior.