This issue has been raised before, but Guido thought that changing things in 2.x would break too much code. See:

http://mail.python.org/pipermail/python-dev/2005-February/051770.html http://mail.python.org/pipermail/python-dev/2005-December/058498.html http://bugs.python.org/issue504714 I'm bringing this up again because the arguments I've seen in favour of fixing hasattr have been fairly weak, and I'd like to raise some stronger ones. Also, I haven't seen this issue considered specifically in the context of Python 3000. The problem is that hasattr behaves just like the following code: def hasattr(obj, name): try: getattr(obj, name) return True except: return False In Python 3000, all exceptions inherit from BaseException, so this is equivalent to: def hasattr(obj, name): try: getattr(obj, name) return True except BaseException: return False There are three major things that are broken by this behaviour, which I don't think have been explicitly mentioned: 1. If the Python interpreter receives SIGINT (usually triggered by Ctrl-C) while executing obj.__getattr__ (or anything it calls), hasattr silently returns False and the program continues running. Cause: KeyboardInterrupt is swallowed. 2. If sys.exit is called within obj.__getattr__, hasattr silently returns False and the program continues running. Cause: SystemExit is swallowed. 3. If an assert statement fails within obj.__getattr__, hasattr silently returns False and the program continues running. Cause: AssertionError is swallowed. Also, because getattr(x,y,z) swallows only AttributeError, users naturally expect hasattr to behave the same way. (This argument has been raised before.) I propose a few alternate behaviours for hasattr (and their consequences): 1. Swallow only AttributeError. - KeyboardInterrupt, SystemExit, and AssertionError are all passed through, solving all three of the above problems. - The behaviour of hasattr is made consistent with getattr(x,y,z). 2. Swallow only Exception. - KeyboardInterrupt and SystemExit are passed through, but AssertionError is still swallowed. - Breaks less code than the previous option. 3. Swallow Exception unless it's an AssertionError. - KeyboardInterrupt, SystemExit, and AssertionError are all passed through, solving all three of the above problems. - Kind of ugly. 4. Swallow everything except KeyboardInterrupt and SystemExit. - AssertionError is still swallowed, but the other problems are fixed and this probably won't break any existing code. I looked at bltinmodule.c, and any of these would be trivial to implement. Ideally, I would like to see the first option implemented in Python 3000 and one of the other options implemented in 2.x. -- Dwayne C. Litzenberger <[EMAIL PROTECTED]> _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com