AttributeError: 'IntegrityError' object has no attribute '__traceback__'

[thomasgoirand]

Hi.

Could you please follow-up on the opened Debian bug here?
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=802677

Cheers,

Thomas

[jml]

Hi Thomas,

I don't have ready access to the Debian BTS, so I'm going to update here.

I don't 100% know what's going on here, but I think it is an issue with traceback2 which we started to exhibit after 55278e0 when we started to depend on it.

https://github.com/testing-cabal/traceback2/blob/master/traceback2/__init__.py#L449 assumes that if an exception has a __cause__, then the cause has a traceback. Clearly this assumption does not always hold.

__cause__ is normally set when an exception is re-raised using the new Python 3 raise from syntax. Python 3 correctly takes care of setting __traceback__ on __cause__.

However, it turns out that Django has special code for setting __cause__ on database exceptions:

As per PEP-3134, a __cause__ attribute is set with the original
(underlying) database exception, allowing access to any additional
information provided. (Note that this attribute is available under
both Python 2 and Python 3, although PEP-3134 normally only applies
to Python 3.)

(from exceptions.txt, some markup edits)

I would suggest that:

1. Django should be a little bit better behaved, and at least set __cause__.__traceback__ to None
2. traceback2 should be a bit more tolerant of poorly behaved exceptions, and wrap the access of __traceback__ in a getattr

Hope this helps,
jml

[rbtcollins]

traceback2 is a rolling backport of Python3's traceback module. Per https://docs.python.org/3/library/exceptions.html - "raise new_exc from original_exc

The expression following from must be an exception or None. It will be set as __cause__ on the raised exception."

The expectation in Python 3 is that __cause__ is either None or a valid exception object - which implies the __traceback__ attribute. The likely thing here is that Django is setting __cause__ (non-standard in Python2) without also setting the exceptions __traceback__ - which it needs to do by hand on Python2 (just as it's setting __cause__ by hand)

[rhertzog]

For reference I have opened a ticket on the Django side: https://code.djangoproject.com/ticket/25761

It will likely get fixed but it's not a high priority ticket so you might still want to rework the code to not make this assumption... if Django did the mistake, it's quite possible other projects did something similar.

[rbtcollins]

Thanks; the place to do that would be in testing-cabal/traceback2 (which is the python stdlib code for traceback handling with only the necessary adjustments to work on Python2.