On Mon, Mar 17, 2008 at 5:35 PM, Alexander Belopolsky <[EMAIL PROTECTED]> wrote: > While discussing issue2291, I presented the following argument: > > """ > Consider the following code: > > class x: > pass > class y(x): > pass > try: > raise y > except y: > print "a" > except: > print "b" > > It prints 'b'.
Really? Under which version exactly? On which platform? I cannot reproduce this with either 2.4, 2.5 or 2.6 on OS X. > Now, suppose in preparation for 3.0 transition someone > adds "__metaclass__ = type" to the module with that code. The result: > it prints 'a'. Which one would expect regardless of the metaclass, right? > Since the difference in behavior is in error handling > code, which in my experience is often not thoroughly tested, the bug > introduced by a seemingly innocuous move from old to new style classes > is likely to trigger in the worst possible moment. (For example a wrong > roll-back logic is applied after a failed database commit.) > """ http://bugs.python.org/msg63584 > > This issue is only partially alleviated by the -3 warning because the warning > is not issued unless the error condition raising a new style class not > deriving > from BaseException is actually tested for. > > It is my understanding that subclass check is skipped for new style classes > not derived from BaseException in order to enable the identity check when a > string exception is caught. I have no idea what you are talking about. Can you quote a file, revision and line number where this is done? > With the deprecation of string exceptions, this logic is hard to justify. > > In any case, I believe this issue is either code or documentation bug: > > """ > Exceptions are identified by class instances. The except clause is > selected depending on the class of the instance: it must reference the class > of > the instance or a base class thereof. > """ http://docs.python.org/dev/reference/executionmodel.html#id2 > > I don't see anything in the documentation that would suggest that old and new > class instances should behave differently. Me neither. -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
