On Fri, Jan 30, 2009 at 3:50 PM, Alan Gauld <alan.ga...@btinternet.com> wrote: > "spir" <denis.s...@free.fr> wrote > >> I was not thinking at data hiding or protection, rather at object >> structure >> (or behaviour) specification. First, to the human -- and alse to the >> machine. > > Ah, OK, then in that case I am happier to agree that Python is unusual > (although not unique - Lisp can do the same) in its ability to add new > attributes - and even methods in V3 I believe - to an existing > class/instance.
Python 2.x can add new methods to a user-defined class or instance or redefine existing methods. Ruby and Objective-C also allow adding methods to existing classes. In Python this is called "monkey-patching" and considered a bad idea. In Ruby it is considered a powerful feature and IIUC it is widely used. > Indeed it's perfectly valid to do: > > class Data: pass ## no attributes or methods! > > d1 = Data() > d2 = Data() > > d1.foo = 'something' > d2.bar = 66 Also this: In [6]: def sayFoo(self): print 'foo' In [7]: Data.sayFoo = sayFoo In [8]: d1.sayFoo() foo > Actually Lisp goes further than Python and allows us to switch > inherited classes around in the method resolution lookup etc > at run time, so > > (foo myMethod) > > might call different methods at different places in the same > program (don't do this kiddies, it will make your brain hurt!) With old-style classes, you can assign directly to __bases__. This seems to have been removed for new-style classes. >> there is no real object specification; not even by class: The introduction of Abstract Base Classes in Python 2.6 and 3.0 seems intended to remedy this, giving you a way to specify an interface in the language: http://docs.python.org/whatsnew/2.6.html#pep-3119-abstract-base-classes Kent _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
