Python decorators that are part of a base class cannot be used to decorate member functions in inherited classes

You need to make UpdateGUI a @classmethod, and make your wrapper aware of self. A working example:

class X(object):    @classmethod    def foo(cls, fun):        def wrapper(self, *args, **kwargs):            self.write(*args, **kwargs)            return fun(self, *args, **kwargs)        return wrapper    def write(self, *args, **kwargs):        print(args, kwargs)class Y(X):    @X.foo    def bar(self, x):        print("x:", x)Y().bar(3)# prints:#   (3,) {}#   x: 3

It might be easier to just pull the decorator out of the SubSytem class:(Note that I'm assuming that the self that calls setport is the same self that you wish to use to call updateGUIField.)

def UpdateGUI(fun): #function decorator    def wrapper(self,*args):        self.updateGUIField(*args)        return fun(self,*args)    return wrapperclass SubSystem(object):    def updateGUIField(self, name, value):        # if name in self.gui:        #     if type(self.gui[name]) == System.Windows.Controls.CheckBox:        #         self.gui[name].IsChecked = value #update checkbox on ui         #     elif type(self.gui[name]) == System.Windows.Controls.Slider:        #         self.gui[name].Value = value # update slider on ui         print(name,value)class DO(SubSystem):    @UpdateGUI    def setport(self, port, value):        """Sets the value of Digital Output port "port"."""        passdo=DO()do.setport('p','v')# ('p', 'v')

You've sort of answered the question in asking it: what argument would you expect to get as self if you call SubSystem.UpdateGUI? There isn't an obvious instance that should be passed to the decorator.

There are several things you could do to get around this. Maybe you already have a subSystem that you've instantiated somewhere else? Then you could use its decorator:

subSystem = SubSystem()subSystem.UpdateGUI(...)

But maybe you didn't need the instance in the first place, just the class SubSystem? In that case, use the classmethod decorator to tell Python that this function should receive its class as the first argument instead of an instance:

@classmethoddef UpdateGUI(cls,...):    ...

Finally, maybe you don't need access to either the instance or the class! In that case, use staticmethod:

@staticmethoddef UpdateGUI(...):    ...

Oh, by the way, Python convention is to reserve CamelCase names for classes and to use mixedCase or under_scored names for methods on that class.