bruno at modulix wrote: > class Base(object): > def __init__(self, arg1): > self.attr1 = arg1 > self.dothis() > > def dothis(self): > return self.attr1 > > class Derived(Base): > def __init__(self, arg1, arg2=0): > self.attr2 = arg2 > Base.__init__(self, arg1) > > def dothis(self): > return self.attr1 + self.attr2 > > (snip) > >> Perhaps if the base __init__ calls an overridden >> method, but at that point it sounds to me like something wants >> refactoring. > > Why so ? This is a well-known pattern (template method). I don't see > what's wrong with it.
Apart from the fact that you can delete the method 'dothis' from both classes with no effect on the code? Actually, this is quite an interesting example becaue it wouldn't work in C++: if you tried the same trick the call to dothis from the base constructor (even assuming it is virtual) would actually call Base.dothis. I think you have demonstrated that you can do some things in Python which you simply cannot do in static languages like C++: assigning to derived attributes before calling a base initialiser, and calling a virtual method from a base initialiser. I'm not arguing about that. What I don't have though is an example of code where doing this would actually be a good thing. What I think I'm trying to get at is that I believe that most situations where someone actually tries to do something in the base initialiser which requires calling a virtual method are probably also cases where the initialiser is doing too much: i.e. separating the construction/initialisation from actually doing something is usually a good idea. -- http://mail.python.org/mailman/listinfo/python-list
