Comments (9)
AlexWaygood
commented on September 26, 2024
2
I'm not sure this is exactly the same as the other case ticket since we are speaking about a test runner here.
Ideally, errors should be isolates as much as possible to single test cases.
The context in which the issue is arising is different, but it's the same underlying issue: many places in the stdlib and third-party libraries (including the test runners provided by the stdlib) depend on being able to mutate attributes of exception instances; you'll break a lot of assumptions in a lot of places if you try to create a frozen exception class.
Would it make sense to add a note either in dataclasses or Exception documentation to explicitly mention that Exception subclasses are expected to be mutable and should thus not be frozen (from the dataclass perspective).
I definitely agree that we need to document this better! Let's discuss on the other issue where it would be best to add that documentation, though 👍
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sobolevn
commented on September 26, 2024
1
Since there's no reproducer right now, I am not fully convinced that this is a bug. Exceptions are expected to be mutable. If you drop some parts of an API from the core CPython object, it will raise an expected error.
Do you agree? :)
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sobolevn
commented on September 26, 2024
1
Well, if something is not documented as immutable, it is mutable by default :)
That's how Python is designed.
However, I think that this part:
Regardless, I would expect a test framework to handle that in a way that only fails the offending test and not the entire test run.
makes sense. Probably error reporting here can be better (for all cases, not just this one).
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AlexWaygood
commented on September 26, 2024
1
I'm going to close this as a duplicate of #99856, as it's the same underlying issue that's being discussed (many places in the stdlib assume that exceptions are mutable; using frozen=True for Exception subclasses is generally a bad idea)
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thomascellerier
commented on September 26, 2024
I managed to reproduce it now, run with python3 -m unittest test.py, with test.py being:
from dataclasses import dataclass
import unittest
class TestFrozenDataclassException(unittest.IsolatedAsyncioTestCase):
async def test_frozen_dataclass_exception(self):
@dataclass(frozen=True)
class FrozenException(Exception):
value: int
try:
raise FrozenException(value=123)
except:
raise ValueError("foo")Which results in:
$ python3 --version
Python 3.11.8
$ python3 -m unittest test.py
Traceback (most recent call last):
File "/home/thomas/Projects/themachine/test.py", line 12, in test_frozen_dataclass_exception
raise FrozenException(value=123)
test.TestFrozenDataclassException.test_frozen_dataclass_exception.<locals>.FrozenException
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3.11/unittest/case.py", line 57, in testPartExecutor
yield
File "/usr/lib/python3.11/unittest/case.py", line 623, in run
self._callTestMethod(testMethod)
File "/usr/lib/python3.11/unittest/async_case.py", line 90, in _callTestMethod
if self._callMaybeAsync(method) is not None:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/async_case.py", line 112, in _callMaybeAsync
return self._asyncioRunner.run(
^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/asyncio/runners.py", line 118, in run
return self._loop.run_until_complete(task)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/asyncio/base_events.py", line 654, in run_until_complete
return future.result()
^^^^^^^^^^^^^^^
File "/home/thomas/Projects/themachine/test.py", line 14, in test_frozen_dataclass_exception
raise ValueError("foo")
ValueError: foo
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<frozen runpy>", line 198, in _run_module_as_main
File "<frozen runpy>", line 88, in _run_code
File "/usr/lib/python3.11/unittest/__main__.py", line 18, in <module>
main(module=None)
File "/usr/lib/python3.11/unittest/main.py", line 102, in __init__
self.runTests()
File "/usr/lib/python3.11/unittest/main.py", line 274, in runTests
self.result = testRunner.run(self.test)
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/runner.py", line 217, in run
test(result)
File "/usr/lib/python3.11/unittest/suite.py", line 84, in __call__
return self.run(*args, **kwds)
^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/suite.py", line 122, in run
test(result)
File "/usr/lib/python3.11/unittest/suite.py", line 84, in __call__
return self.run(*args, **kwds)
^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/suite.py", line 122, in run
test(result)
File "/usr/lib/python3.11/unittest/suite.py", line 84, in __call__
return self.run(*args, **kwds)
^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/suite.py", line 122, in run
test(result)
File "/usr/lib/python3.11/unittest/case.py", line 678, in __call__
return self.run(*args, **kwds)
^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/async_case.py", line 131, in run
return super().run(result)
^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/case.py", line 622, in run
with outcome.testPartExecutor(self):
File "/usr/lib/python3.11/contextlib.py", line 158, in __exit__
self.gen.throw(typ, value, traceback)
File "/usr/lib/python3.11/unittest/case.py", line 74, in testPartExecutor
_addError(self.result, test_case, exc_info)
File "/usr/lib/python3.11/unittest/case.py", line 99, in _addError
result.addError(test, exc_info)
File "/usr/lib/python3.11/unittest/runner.py", line 98, in addError
super(TextTestResult, self).addError(test, err)
File "/usr/lib/python3.11/unittest/result.py", line 17, in inner
return method(self, *args, **kw)
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/result.py", line 115, in addError
self.errors.append((test, self._exc_info_to_string(err, test)))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/result.py", line 176, in _exc_info_to_string
tb = self._clean_tracebacks(exctype, value, tb, test)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/unittest/result.py", line 214, in _clean_tracebacks
value.__traceback__ = tb
^^^^^^^^^^^^^^^^^^^
File "<string>", line 4, in __setattr__
dataclasses.FrozenInstanceError: cannot assign to field '__traceback__'
from cpython.
thomascellerier
commented on September 26, 2024
Exceptions are expected to be mutable.
I was trying to find if that was documented anywhere but could not find any definitive documentation, maybe I'm not looking at the right place though.
The python3.11+ exception notes feature certainly relies on mutability as well but I could not find anything in the PEP describing what happens if an exception overrides __setattr__ in way that forbids adding and/or setting an attribute.
Regardless, I would expect a test framework to handle that in a way that only fails the offending test and not the entire test run.
It could even point to the root issue, e.g. "Exception subclasses should be mutable".
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thomascellerier
commented on September 26, 2024
Same in main, but with much nicer colored output :)
thomas@thomas-xps13:~/Projects/cpython$ ./python --version
Python 3.13.0a5+
thomas@thomas-xps13:~/Projects/cpython$ ./python -m unittest test.py
Traceback (most recent call last):
File "/home/thomas/Projects/cpython/test.py", line 12, in test_frozen_dataclass_exception
raise FrozenException(value=123)
test.TestFrozenDataclassException.test_frozen_dataclass_exception.<locals>.FrozenException
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/thomas/Projects/cpython/Lib/unittest/case.py", line 58, in testPartExecutor
yield
File "/home/thomas/Projects/cpython/Lib/unittest/case.py", line 634, in run
self._callTestMethod(testMethod)
~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/async_case.py", line 93, in _callTestMethod
if self._callMaybeAsync(method) is not None:
~~~~~~~~~~~~~~~~~~~~^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/async_case.py", line 115, in _callMaybeAsync
return self._asyncioRunner.run(
~~~~~~~~~~~~~~~~~~~~~~~^
func(*args, **kwargs),
^^^^^^^^^^^^^^^^^^^^^^
context=self._asyncioTestContext,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "/home/thomas/Projects/cpython/Lib/asyncio/runners.py", line 118, in run
return self._loop.run_until_complete(task)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "/home/thomas/Projects/cpython/Lib/asyncio/base_events.py", line 721, in run_until_complete
return future.result()
~~~~~~~~~~~~~^^
File "/home/thomas/Projects/cpython/test.py", line 14, in test_frozen_dataclass_exception
raise ValueError("foo")
ValueError: foo
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/thomas/Projects/cpython/Lib/runpy.py", line 198, in _run_module_as_main
return _run_code(code, main_globals, None,
~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
"__main__", mod_spec)
^^^^^^^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/runpy.py", line 88, in _run_code
exec(code, run_globals)
~~~~^^^^^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/__main__.py", line 18, in <module>
main(module=None)
~~~~^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/main.py", line 104, in __init__
self.runTests()
~~~~~~~~~~~~~^^
File "/home/thomas/Projects/cpython/Lib/unittest/main.py", line 270, in runTests
self.result = testRunner.run(self.test)
~~~~~~~~~~~~~~^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/runner.py", line 240, in run
test(result)
~~~~^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/suite.py", line 84, in __call__
return self.run(*args, **kwds)
~~~~~~~~^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/suite.py", line 122, in run
test(result)
~~~~^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/suite.py", line 84, in __call__
return self.run(*args, **kwds)
~~~~~~~~^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/suite.py", line 122, in run
test(result)
~~~~^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/suite.py", line 84, in __call__
return self.run(*args, **kwds)
~~~~~~~~^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/suite.py", line 122, in run
test(result)
~~~~^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/case.py", line 690, in __call__
return self.run(*args, **kwds)
~~~~~~~~^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/async_case.py", line 134, in run
return super().run(result)
~~~~~~~~~~~^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/case.py", line 633, in run
with outcome.testPartExecutor(self):
self._callTestMethod(testMethod)
File "/home/thomas/Projects/cpython/Lib/contextlib.py", line 162, in __exit__
self.gen.throw(value)
~~~~~~~~~~~~~~^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/case.py", line 75, in testPartExecutor
_addError(self.result, test_case, exc_info)
~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/case.py", line 100, in _addError
result.addError(test, exc_info)
~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/runner.py", line 101, in addError
super(TextTestResult, self).addError(test, err)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/result.py", line 17, in inner
return method(self, *args, **kw)
~~~~~~^^^^^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/result.py", line 116, in addError
self.errors.append((test, self._exc_info_to_string(err, test)))
~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/result.py", line 188, in _exc_info_to_string
tb = self._clean_tracebacks(exctype, value, tb, test)
~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/result.py", line 226, in _clean_tracebacks
value.__traceback__ = tb
^^^^^^^^^^^^^^^^^^^
File "<string>", line 4, in __setattr__
dataclasses.FrozenInstanceError: cannot assign to field '__traceback__'
thomas@thomas-xps13:~/Projects/cpython$ git rev-parse HEAD
eebea7e515462b503632ada74923ec3246599c9c
from cpython.
thomascellerier
commented on September 26, 2024
This small patch avoids this problem, though of course I'm not sure of any other implications here:
thomas@thomas-xps13:~/Projects/cpython$ ./python -m unittest test.py
EE
======================================================================
ERROR: test_frozen_dataclass_exception (test.TestFrozenDataclassException.test_frozen_dataclass_exception)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/thomas/Projects/cpython/test.py", line 12, in test_frozen_dataclass_exception
raise FrozenException(value=123)
test.TestFrozenDataclassException.test_frozen_dataclass_exception.<locals>.FrozenException
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/thomas/Projects/cpython/Lib/unittest/async_case.py", line 93, in _callTestMethod
if self._callMaybeAsync(method) is not None:
~~~~~~~~~~~~~~~~~~~~^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/async_case.py", line 115, in _callMaybeAsync
return self._asyncioRunner.run(
~~~~~~~~~~~~~~~~~~~~~~~^
func(*args, **kwargs),
^^^^^^^^^^^^^^^^^^^^^^
context=self._asyncioTestContext,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "/home/thomas/Projects/cpython/Lib/asyncio/runners.py", line 118, in run
return self._loop.run_until_complete(task)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "/home/thomas/Projects/cpython/Lib/asyncio/base_events.py", line 721, in run_until_complete
return future.result()
~~~~~~~~~~~~~^^
File "/home/thomas/Projects/cpython/test.py", line 14, in test_frozen_dataclass_exception
raise ValueError("foo")
ValueError: foo
======================================================================
ERROR: test_other (test.TestFrozenDataclassException.test_other)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/thomas/Projects/cpython/Lib/unittest/async_case.py", line 93, in _callTestMethod
if self._callMaybeAsync(method) is not None:
~~~~~~~~~~~~~~~~~~~~^^^^^^^^
File "/home/thomas/Projects/cpython/Lib/unittest/async_case.py", line 120, in _callMaybeAsync
return self._asyncioTestContext.run(func, *args, **kwargs)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
TypeError: TestFrozenDataclassException.test_other() takes 0 positional arguments but 1 was given
----------------------------------------------------------------------
Ran 2 tests in 0.015s
FAILED (errors=2)
thomas@thomas-xps13:~/Projects/cpython$ git diff
diff --git a/Lib/unittest/result.py b/Lib/unittest/result.py
index 3ace0a5..da32563 100644
--- a/Lib/unittest/result.py
+++ b/Lib/unittest/result.py
@@ -223,7 +223,11 @@ def _clean_tracebacks(self, exctype, value, tb, test):
ret = tb
first = False
else:
- value.__traceback__ = tb
+ try:
+ value.__traceback__ = tb
+ except AttributeError:
+ # Attribute is not settable in exception class
+ pass
if value is not None:
for c in (value.__cause__, value.__context__):from cpython.
thomascellerier
commented on September 26, 2024
I'm not sure this is exactly the same as the other case ticket since we are speaking about a test runner here.
Ideally, errors should be isolates as much as possible to single test cases.
Would it make sense to add a note either in dataclasses or Exception documentation to explicitly mention that Exception subclasses are expected to be mutable and should thus not be frozen (from the dataclass perspective).
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