Make ValidationError Hashable #477

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1. Julian commented on Oct 17, 2018

   

   Julian

   on Oct 17, 2018

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   Hey yeah this is one of the remaining things I'm thinking about before the release.

   The issue with making them hashable is that doing so requires an API change, because they've got mutable attributes on them at the minute, so those would need to become immutable ones.

   👍React with 👍2Reacted by Sujan and Stuart Berg
2. Julian

   changed the title [-]can't logging.exception(ValidationError), raises Exception TypeError: unhashable type: 'ValidationError'[/-] [+]Make ValidationError Hashable[/+] on Nov 2, 2018
3. Julian

   added

   EnhancementSome new desired functionalitySome new desired functionality

   on Nov 2, 2018
4. stuarteberg commented on Nov 30, 2018

   

   stuarteberg

   on Nov 30, 2018

   Last edited by stuarteberg

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   Of course, ValidationError and SchemaError would be trivially hashable if they didn't define __eq__. Is it necessary for those classes to be comparable? I tried grepping the jsonschema code base for == and !=, and as far as I can tell, exceptions are never explicitly compared. (But I could definitely be missing implicit comparisons, such as if exc in mylist:, etc.)

   If comparability is not necessary, I vote for simply removing _Error.__eq__() and _Error.__ne__().

   For now, here's my workaround:

   from jsonschema.exceptions import _Error
   _Error.__eq__ = object.__eq__
   _Error.__ne__ = object.__ne__
   _Error.__hash__ = object.__hash__

   ---

   Making the exceptions hashable would be great to use in standard logging libraries.

   Here's another use-case: pytest can't handle unhashable exceptions, so any users whose tests might raise a ValidationError will currently see an INTERNALERROR traceback from pytest, crashing the whole test suite.

   For example:

   # test.py
   from jsonschema import validate
   def test():
       validate([], {"type": "object"})

   $ pytest test.py
   
   ...
   
   INTERNALERROR>   File "/prefix/lib/python3.6/site-packages/_pytest/_code/code.py", line 398, in exconly
   INTERNALERROR>     lines = format_exception_only(self.type, self.value)
   INTERNALERROR>   File "/prefix/lib/python3.6/traceback.py", line 136, in format_exception_only
   INTERNALERROR>     return list(TracebackException(etype, value, None).format_exception_only())
   INTERNALERROR>   File "/prefix/lib/python3.6/traceback.py", line 462, in __init__
   INTERNALERROR>     _seen.add(exc_value)
   INTERNALERROR> TypeError: unhashable type: 'ValidationError'
   

   👍React with 👍1Reacted by John Hagen
5. Julian commented on Dec 4, 2018

   

   Julian

   on Dec 4, 2018

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   It's used in tests, yes, via assertEqual.

   Here's another use-case: pytest can't handle unhashable exceptions, so any users whose tests might raise a ValidationError will currently see an INTERNALERROR traceback from pytest, crashing the whole test suite.

   Sounds like a py.test bug worth filing regardless, though presumably it's just the same underlying one (that py~34-36 broke this, and then fixed it again in 3.7). pytest seems like the sort of thing though that should be trying to fix it even on those though.
6. stuarteberg

   added 3 commits that reference this issue on Dec 6, 2018

   Make exceptions hashable (but not comparable)

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   This issue will close once commit c0c9de2 is merged into the 'master' branch.

   c0c9de2

   Make exceptions hashable (but not comparable)

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   This issue will close once commit 2c83d78 is merged into the 'master' branch.

   2c83d78

   Make exceptions hashable (but not comparable)

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   This issue will close once commit f9995aa is merged into the 'master' branch.

   f9995aa
7. stuarteberg commented on Dec 6, 2018

   

   stuarteberg

   on Dec 6, 2018

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   It's used in tests, yes, via assertEqual.

   Ah, thanks for pointing that out. Still, it's not used in many places, so I've proposed #502 to eliminate the need for comparable exceptions.

   Sounds like a py.test bug worth filing regardless

   OK, I've submitted pytest-dev/pytest#4514, to see if they're interested in supporting unhashable exceptions.
8. stuarteberg

   added a commit that references this issue on Dec 6, 2018

   Make exceptions hashable (but not comparable)

   ...

   This issue will close once commit a7ca0c5 is merged into the 'master' branch.

   a7ca0c5
9. stuarteberg commented on Dec 6, 2018

   

   stuarteberg

   on Dec 6, 2018

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   presumably it's just the same underlying one (that py~34-36 broke this, and then fixed it again in 3.7)

   FWIW, you're right: This is not an issue when using Python 3.7. I'm using Python 3.6, where it is an issue.
10. Julian

    closed this as completedin a7ca0c5on Dec 15, 2018
11. Julian

    added a commit that references this issue on Apr 28, 2021

    Squashed 'json/' changes from 15ec577f..09fd353f

    ...

    c19f0b4