[Python-Dev] Exception and ABCs / issue #12029 (original) (raw)

Guido van Rossum guido at python.org
Fri May 11 18:38:34 CEST 2012

Thanks for bringing this up. I've added my opinion to the tracker issue -- I think it's a bug and should be fixed. We should have a uniform way of checking for issubclass/isinstance.

--Guido

On Fri, May 11, 2012 at 3:33 AM, George-Cristian Bîrzan <gcbirzan at gmail.com> wrote:

As per http://bugs.python.org/issue12029 , ABC registration cannot be used for exceptions. This was introduced in a commit that fixed a recursion limit problem back in 2008 (http://hg.python.org/cpython/rev/d6e86a96f9b3/#l8.10). This was later fixed in a different way and improved upon in the 2.x branch in http://hg.python.org/cpython/rev/7e86fa255fc2 and http://hg.python.org/cpython/rev/57de1ad15c54 respectively.

Applying the fix from the 2.x branch for doesn't make any tests fail, and it fixes the problem described in the bug report. There are, however, two questions about this: * Is this a feature, or a bug? I would say that it's a bug, but even if it's not, it has to be documented, since one generally assumes that it will work. * Even so, is it worth fixing, considering the limited use cases for it? This slows exception type checking 3 times. I added a new test to pybench: before: TryRaiseExceptClass:     25ms     25ms    0.39us    0.216ms after: TryRaiseExceptException:     31ms     31ms    0.48us    0.214ms However, that doesn't tell the whole story, since there's overhead from raising the exception. In order to find out how much actually checking slows down the checking, I ran three timeits, with the following code: 1) try: raise ValueError() except NameError: pass except NameError: pass except ValueError: pass 2) try: raise ValueError() except NameError: pass except ValueError: pass 3) try: raise ValueError() except ValueError: pass Times are in ms: before      after 1       528.69      825.38 2       473.73      653.39 3       416.29      496.80 avgdiff  56.23      164.29 The numbers don't change significantly for more exception tests. -- George-Cristian Bîrzan

Python-Dev mailing list Python-Dev at python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/guido%40python.org

-- --Guido van Rossum (python.org/~guido)

More information about the Python-Dev mailing list