Andrew Jaffe wrote: >>Andrew Jaffe wrote: >> >> >>>Hi, >>> >>>I have a class with various class-level variables which are used to >>>store global state information for all instances of a class. These are >>>set by a classmethod as in the following >>> >>>class sup(object): >>> cvar1 = None >>> cvar2 = None >>> >>> @classmethod >>> def setcvar1(cls, val): >>> cls.cvar1 = val >>> >>> @classmethod >>> def setcvar2(cls, val): >>> cls.cvar2 = val >>> >>> @classmethod >>> def printcvars(cls): >>> print cls.cvar1, cls.cvar2 >>> >>>Now, the problem comes when I want to subclass this class. If I >>>override the setcvar1 method to do some new things special to this >>>class, and then call the sup.setcvar1() method, it all works fine: >>> >>>class sub(sup): >>> cvar1a = None >>> >>> @classmethod >>> def setcvar1(cls, val, vala): >>> cls.cvar1a = vala >>> sup.setcvar1(val) >>> >>> @classmethod >>> def printcvars(cls): >>> print cls.cvar1a >>> sup.printcvars() >>> >>>This works fine, and sets cvar and cvar2 for both classes. >>> >>>However, if I *don't* override the setcvar2 method, but I call >>>sub.setcvar2(val) directly, then only sub.cvar2 gets set; it is no >>>longer identical to sup.cvar1! >>> >>>In particular, >>> sub.setcvar1(1,10) >>> sub.setcvar2(2) >>> sub.printcvars() >>>prints >>> 10 >>> 1 None >>> >>>i.e. sub.cvar1, sub.cvar1a, sub.cvar2= 1 10 2 >>>but sup.cvar1, cvar2= 1 None >>> >>>This behavior is "expected", but is it desirable? >>> >> >>You are experiencing this problem because you are using hard-wired class >>names. Try using (for example) self.__class__. That way, even if your >>method is inheroted by a subclass it will use the class of the object it >>finds itself a method of. No need to use classmethods. > > > The problem is that I actually do want to call these methods on the > class itself, before I've made any instances. > I see. I think. So what you are saying is that when you call sup.printcvars() from inside a sub method you want it to see the namespace of the sub class not the sup?
Since you have set all this up carefully you must have a use case, but it seems a little contorted (to me). Basically you appear to want the classes to behave statically the way that instances do dynamically? Not sure I can help you 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
