python class methods and inheritance

Question

I would expect the following code to print 012345 but it prints 012012. Why? I would expect the calls to incr to be accessing the same variables since they are inherited fro

Answer 1

There is a way to produce the sequence 012345. You have to make sure that the var of class a is increased in the incr method, even when it is called in the subclasses. To achieve this, increment by a.var += 1, not by cls.var += 1.

As pointed out by the other answers, the var is also inherited to b and c. By using cls.var += 1 both subclasses increase their own var instead of a's var.

class a:
    var = 0
    @classmethod
    def incr(cls):
        print(cls.var)
        a.var += 1

class b(a):
    def f(self):
        super().incr()

class c(a):
    def f(self):
        super().incr()

cb = b()
cc = c()
cb.incr()
cb.incr()
cb.incr()
cc.incr()
cc.incr()
cc.incr()

cb.incr()
cc.incr()

Produces:

0
1
2
3
4
5
6
7