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gh-113358: Fix rendering tracebacks with exceptions with a broken __getattr__ #113359

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Merged
vsajip merged 5 commits into from
Jan 16, 2024
Merged

gh-113358: Fix rendering tracebacks with exceptions with a broken __getattr__ #113359

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1f40d5f
Fix rendering tracebacks with exceptions with a broken __getattr__
perrinjerome Dec 21, 2023
9eed42e
📜🤖 Added by blurb_it.
blurb-it[bot] Dec 21, 2023
8651d3e
Display error accessing __notes__ along with the traceback
perrinjerome Jan 15, 2024
6ecf82d
fixup! Display error accessing __notes__ along with the traceback
perrinjerome Jan 15, 2024
6c6867a
Apply suggestions from code review
perrinjerome Jan 15, 2024
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12 changes: 12 additions & 0 deletions Lib/test/test_traceback.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2209,6 +2209,18 @@ def __repr__(self):
err_msg = "b'please do not show me as numbers'"
self.assertEqual(self.get_report(e), vanilla + err_msg + '\n')

# an exception with a broken __getattr__ raising a non expected error
class BrokenException(Exception):
broken = False
def __getattr__(self, name):
if self.broken:
raise ValueError(f'no {name}')

e = BrokenException(123)
vanilla = self.get_report(e)
e.broken = True
self.assertEqual(self.get_report(e), vanilla)

def test_exception_with_multiple_notes(self):
for e in [ValueError(42), SyntaxError('bad syntax')]:
with self.subTest(e=e):
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7 changes: 6 additions & 1 deletion Lib/traceback.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1051,7 +1051,12 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
# Capture now to permit freeing resources: only complication is in the
# unofficial API _format_final_exc_line
self._str = _safe_string(exc_value, 'exception')
self.__notes__ = getattr(exc_value, '__notes__', None)
notes = None
try:
notes = getattr(exc_value, '__notes__', None)
except Exception:
pass

@iritkatriel iritkatriel Dec 21, 2023

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We don't swallow exceptions like this. What is your use case for defining an exception with a broken __getattr__?

@terryjreedy terryjreedy Dec 21, 2023

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I had much the same question on the issue. Python reporting bugs in user code does not seem like a python bug. OP needs to justify the python bug claim by quoting doc that says that user exceptions will by caught, or make this a feature request, with justification.

@perrinjerome perrinjerome Dec 22, 2023

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Thank you for your feedback, I am sorry I did not explain enough. I have tried to add more context to the issue.

About not swallowing exceptions, I don't like it either (and I understand the negative feedback), maybe this patch should be adjusted to at least report that an exception occurred while getting the notes, by doing something like this instead ?

        try:
            self.__notes__ = getattr(exc_value, '__notes__', None)
        except Exception as e:
            self.__notes__ = [
                f'Ignored exception getting __notes__: {_safe_string(e, '__notes__', repr)}']

@serhiy-storchaka serhiy-storchaka Dec 22, 2023

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Unfortunately we do swallow exceptions like this. _safe_string() set a bad precedence since 2823f03.

@perrinjerome perrinjerome Jan 15, 2024

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I have updated the patch to include the "Ignored exception getting notes ..." in the notes as suggested above, from the discussion on the issue it seemed better to include information about the error in that case.

self.__notes__ = notes

self._is_syntax_error = False
self._have_exc_type = exc_type is not None
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2023-12-21-14-55-06.gh-issue-113358.nRkiSL.rst
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@@ -0,0 +1 @@
Fix rendering tracebacks with exceptions with a broken __getattr__