On Apr 27, 9:20 pm, alex23 <wuwe...@gmail.com> wrote: > GZ <zyzhu2...@gmail.com> wrote: > > I do not think it will help me. I am not trying to define a function > > fn() in the class, but rather I want to make it a "function reference" > > so that I can initialize it any way I like later. > > It always helps to try an idea out before dismissing it out of hand. > Experimentation in the interpreter is cheap and easy. > > >>> class A(object): > > ... fn = staticmethod(lambda x: x*x) > ...>>> A.fn(10) > 100 > >>> A.fn = staticmethod(lambda x: x**x) > >>> A.fn(3) > 27 > >>> def third(x): return x/3 > ... > >>> A.fn = staticmethod(third) > >>> A.fn(9) > > 3 > > However, I'm assuming you're wanting to do something like this: > > >>> class B(object): > > ... def act(self): > ... print self.fn() > > That is, providing a hook in .act() that you can redefine on demand. > If so, note that you only need to decorate functions as staticmethods > if you're assigning them to the class. If you intend on overriding on > _instances_, you don't: > > >>> B.fn = staticmethod(lambda: 'one') # assign on class > >>> b = B() # instantiate > >>> b.act() # act on instance > one > >>> B.fn = staticmethod(lambda: 'two') # assign on class > >>> b.act() # existing instance calls new version on class > two > >>> b.fn = staticmethod(lambda: 'three') # assign on instance > >>> b.act() > > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > File "<stdin>", line 3, in act > TypeError: 'staticmethod' object is not callable>>> b.fn = lambda: 'three' # > look Ma, no staticmethod! > >>> b.act() > > three > > Incidentally, this is known as the Strategy pattern, and you can see a > simple example of it in Python > here:http://en.wikipedia.org/wiki/Strategy_pattern#Python > > Hope this helps.
Ah, this totally works. The key is to use the staticmethod function. Thanks a lot. -- http://mail.python.org/mailman/listinfo/python-list
