On Oct 9, 9:16 am, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > Hi. > > I've got a question on the differences and how to define static and > class variables. AFAIK, class methods are the ones which receives the > class itself as an argument, while static methods are the one which > runs statically with the defining class. > > Hence, my understanding is that static variables must be bound to the > class defining the variables and shared by children of parent class > where the variable is defined. But, please have a look at this code in > which a guy told me that the variable a is static: > > >>> class Foo: > > a = 1 > @classmethod > def increment(cls): > cls.a += 1 > print cls.a > > Here, I am defining variable a which, I believe is class variable, > i.e., variable that is not bound to Foo itself. Rather, a is bound to > the class which is accessing the variable. The code that corroborates > this idea is as follows: > > >>> class Child1(Foo): > > pass > > >>> Child1.increment() > > 4 > > >>> class Child2(Foo): > > pass > > >>> Child2.increment() > > 4 > > This means that Child1 and Child2 does not share variable a which > means that variable a is class variable rather than static variable. > > Could you please comment on this? Is a static or class variable? > What's the most recent way of defining 'class' and 'static' variables?
In Python `a' is considered a class variable. By modifying `a' using a class method though, you are essentially re-binding `a' to the class that it is called from. So, it will be shared by multiple instances of the same class, but not derivatives. The re-binding only occurs when `increment' is called. This makes for some very confusing behavior. I'm not aware of a way, in python, to explicitly specify a variable as static. For the behavior I think you are looking for you just need to modify it carefully. This can be done with a static, class or instance method. Though, using a class method is kind of silly. I'm sure some would argue that using an instance method is also silly. code: class C(object): a = 0 def inc(self): C.a += 1 # directly modify the variable on the base class that it is attached to return C.a # or you could use a static method, which is fine since the instance isn't being used. This # will also allow the method to be called without instantiating the class. class C(object): a = 0 @staticmethod def inc(): C.a += 1 return C.a Matt -- http://mail.python.org/mailman/listinfo/python-list
