Andrew Jaffe wrote: > Steve Holden wrote: > >>Andrew Jaffe wrote: >> >>>Steve Holden wrote: >>> >>>>Andrew Jaffe wrote: >>>> >>>> >>>>>The problem is that I actually do want to call these methods on the >>>>>class itself, before I've made any instances. >>>>> >>>> >>>>Except you could use staticmethods with an explicit class argument ... >>> >>>Yep, that would work! Thanks. >>> >>>But it does seem like a bit of a kludge: classmethods seems to be >>>almost exactly what you 'ought' to use here (i.e., I really do want to >>>apply these methods to the class as an object in its own right). >>> >> >>What's the use case? > > > Fair question. I hope the following isn't too technical. > > I have a class which describes the model for fitting some data, > encapsulating among other things a bunch of parameters whose values I'd > like to determine for a given dataset. The base class is a simple model, > the derived class a slightly more complicated one with an extra parameter. > > At present, I instantiate the class with a particular set of values for > the parameters. > > One of the methods in this class is called 'prior', which returns the > prior probability for the instance's paramters. > > However, it turns out there are some 'meta-parameters' which don't > change between instances, in particular the allowed limits on the > parameters, beyond which the prior should return 0. Currently these are > stored as class variables -- so both the base and derived class want to > be able to act as if these class variables are 'native' to their own > class -- since in fact the base/derived relationship is in this case > actually something of an implementation detail. (Currently I've solved > the problem by explicitly using the base class methods for setting the > class variables.) > > Does this make sense? >
I think so. It's not normal adive, but it sounds like a metaclass might be what you need here. regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC www.holdenweb.com PyCon TX 2006 www.python.org/pycon/ -- http://mail.python.org/mailman/listinfo/python-list
