After upgrading to 3.10a5, calling logging.exception("test") results in:

--- Logging error \---

    Traceback (most recent call last):
      File "/usr/lib/python3.10/logging/__init__.py", line 1094, in emit
        msg = self.format(record)
      File "/usr/lib/python3.10/logging/__init__.py", line 938, in format
        return fmt.format(record)
      File "/usr/lib/python3.10/logging/__init__.py", line 682, in format
        record.exc_text = self.formatException(record.exc_info)
      File "/usr/lib/python3.10/logging/__init__.py", line 632, in formatException
        traceback.print_exception(ei[0], ei[1], tb, None, sio)
      File "/usr/lib/python3.10/traceback.py", line 113, in print_exception
        te = TracebackException(type(value), value, tb, limit=limit, compact=True)
      File "/usr/lib/python3.10/traceback.py", line 531, in __init__
        need_context = cause is None and not e.__suppress_context__
    AttributeError: 'NoneType' object has no attribute '__suppress_context__'

That method is documented as "This function should only be called from an exception handler.", but the same also happens when e.g. calling traceback.print_exc() (without a current exception) or traceback.print_exception(None, None, None). Both worked fine before 3.10 Alpha 5, the code seems to do None-checks in other places, and typeshed also marks those arguments as Optional.

This seems to have been introduced in #24179 for bpo-42877.

Thanks, I’ll add the None check.

There's another such issue due to PR 22610 // bpo-26389:

>>> traceback.format_exception(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\User\src\cpython-dev\lib\traceback.py", line 128, in format_exception
    value, tb = _parse_value_tb(exc, value, tb)
  File "C:\Users\User\src\cpython-dev\lib\traceback.py", line 94, in _parse_value_tb
    return exc, exc.__traceback__
AttributeError: 'NoneType' object has no attribute '__traceback__'

Marking as blocker because these are 3.10 regressions.

It seems to me that print_exception(None), etc, *should* raise something. Printing "NoneType: None\n" makes no sense to me since NoneType is not an exception. In 3.9, it raised TypeError for # of arguments.

I do note that in 3.9
>>> traceback.print_exception(None, None, None)
NoneType: None

I wonder what the rationale was. It isn't because these functions never raise.

In 3.9 you had to give exc,val,tb. In 3.10 the shortcut was added. bpo-26389.

JFYI, there are 2 affected Fedora packages (that we know of):

visidata fails to build with Python 3.10: AttributeError: 'NoneType' object has no attribute '__suppress_context__'
https://bugzilla.redhat.com/show_bug.cgi?id=1928145

python-utils fails to build with Python 3.10: AttributeError: 'NoneType' object has no attribute '__suppress_context__'
https://bugzilla.redhat.com/show_bug.cgi?id=1928081

I wonder what the rationale was. It isn't because these functions never raise.

I think it's because sys.exc_info() can return None, None, None when there is no exceptions.

Let's split the print_exception(None) case (new issue) from the regression. I've updated the PR to fix only the latter, which is not controversial.

I don't know what print_exception(None) should do.

New changeset 26f18b8 by Irit Katriel in branch 'master':
bpo-43146: fix regression in traceback.print_exception(None) (GH-24463)
26f18b8

Are you going to create a separate PR or a new issue for the other thing? (And what exactly *is* the other thing? Please summarize.)

The other thing is not related to the one reported here, but I found it while writing the test for this.

We have a new API in 3.10, where you can do traceback.print_exception(ex) (so you don't need to give the whole type,val,tb triplet).

But:

>>> traceback.print_exception(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\User\src\cpython-dev\lib\traceback.py", line 110, in print_exception
    value, tb = _parse_value_tb(exc, value, tb)
  File "C:\Users\User\src\cpython-dev\lib\traceback.py", line 94, in _parse_value_tb
    return exc, exc.__traceback__
AttributeError: 'NoneType' object has no attribute '__traceback__'

So the PR just merged fixes that, right? Color me confused.

The PR just merged fixes the issue that was reported by Florian (what I broke). That impacted pre-3.10 APIs so was an actual regression.

The issue with traceback.print_exception(None) is new to 3.10, and was introduced in bpo-26389.

So the remaining question is what to do for print_exception(None)? Honestly
the current (new) behavior of printing NoneType: None seems fine.

So the remaining question is what to do for print_exception(None)?

Yes.

Honestly the current (new) behavior of printing NoneType: None seems fine.

That's not the current behaviour - I removed that fix from the PR till we agree what to do. Currently we get the AttributeError.

The new PR makes it print NoneType: None, which is at least consistent with what the same functions do without the bpo-26389 shortcut.

New changeset b798ab0 by Irit Katriel in branch 'master':
bpo-43146: fix None-handling in single-arg traceback.print_exception(None) (GH-24629)
b798ab0