On Sat, Mar 28, 2009 at 10:21 AM, Mathias Panzenböck <grosser.meister.morti@gmx.net> wrote:
Péter Szabó wrote:
If Python had method decorators @final (meaning: it is an error to override this method in any subclass) and @override (meaning: it is an error not having this method in a superclass), I would use them in my projects (some of them approaching 20 000 lines of Python code) and I'll feel more confident writing object-oriented Python code. Java already has similar decorators or specifiers. Do you think it is a good idea to have these in Python?
I've created a proof-of-concept implementation, which uses metaclasses, and it works in Python 2.4 an Python 2.5. See http://www.math.bme.hu/~pts/pobjects.py and http://www.math.bme.hu/~pts/pobjects_example.py
Best regards,
Péter
+1 on the idea. however, using a metaclass would be to limiting imho. can you implement it in a different way? a lot of things people use metaclasses for work perfectly fine without them (instead use a superclass that overrides __new__ or similar).
While it could be done by overriding __new__ in a superclass I'm not sure how that would make it easier to use, and it would make it harder to implement efficiently: this is a check that you would like to happen once at class definition time rather than on each instance creation. Of course you could do some caching to do it at the first instantiation only, but that still sounds clumsy; the metaclass is the obvious place to put this, and gives better error messages (at import instead of first use). But I don't think this idea is ripe for making it into a set of builtins yet, at least, I would prefer if someone coded this up as a 3rd party package and got feedback from a community of early adopters first. Or maybe one of the existing frameworks would be interested in adding this? While this may not be everyone's cup of tea (e.g. Scott David Daniels' reply), some frameworks cater to users who do like to be told when they're making this kind of errors. -- --Guido van Rossum (home page: http://www.python.org/~guido/)