python class static method dynamic binding static data member

Question

I really don't know how to describe this problem good enough. So i think an example is more expressive:

class A:
    c=1
    @staticmethod
    def b(): return A.c

class B(A):
    c=2

I hope B.b() returns 2. but the reality is it does not. in which way am i gonna achieve it? Thanks a lot.

If you want to access a class attribute, why are you using a staticmethod instead of a classmethod? — BrenBarn, Oct 10 '14 at 19:16

score 2 · Answer 1 · answered Oct 10 '14 at 19:16

You'd have to use a class method, so you could reference the class dynamically. A static method like you are currently using is not bound to any class, so you have to statically explicitly reference the A class as you are.

class A(object):
    c = 1
    @classmethod
    def b(cls):
        return cls.c

class B(A):
    c = 2

score 2 · Accepted Answer · edited May 23 '17 at 11:57

The problem is that you're using a staticmethod, and hardcoding the class A, instead of using a classmethod, and using the cls argument.

Try this:

class A:
    c=1
    @classmethod
    def b(cls): return cls.c

The docs (linked above) explain the difference, but you may want to try looking at Stack Overflow questions like What is the difference between @staticmethod and @classmethod in Python for a more in-depth discussion. Briefly: a staticmethod is basically just a global function inside the class's namespace, while a classmethod is a method on the class object; if you want to use any class attributes (or the class itself, as in the alternate constructor idiom), you want the latter.

python class static method dynamic binding static data member

2 Answers2