TypeError when except* catches an unhashable exception

[Zac-HD]

I recently had pytest-dev/pytest#10466 reported, and it seems likely to be an upstream bug in except* - cc @iritkatriel fyi.
A somewhat simplified reproducing example:

class MyException(Exception):
    __hash__ = None

# Traditional try-except works fine with unhashable exceptions, e.g.:
try:
    raise ExceptionGroup("Foo", [MyException("Bar")])
except Exception:
    pass

# But here we'll get a TypeError:
try:
    raise ExceptionGroup("Foo", [MyException("Bar")])
except* Exception:
    pass

  + Exception Group Traceback (most recent call last):
  |   File "repro.py", line 12, in <module>
  |     raise ExceptionGroup("Foo", [MyException("Bar")])
  | ExceptionGroup: Foo (1 sub-exception)
  +-+---------------- 1 ----------------
    | MyException: Bar
    +------------------------------------

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "repro.py", line -1, in <module>
TypeError: unhashable type: 'MyException'

If this is the intended behavior of course we'll work around it in Pytest, but we decided to report upstream in case it's not 🙂

• PR: gh-99181: fix except* on unhashable exceptions #99192

• PR: [3.11] gh-99181: fix except* on unhashable exceptions (GH-99192) #99243

[iritkatriel]

Yes it’s a bug. Thanks.