如何从父方法引用子类？

Question

In the following sample, is there a magic word I can put in place of <ChildClass> that works like the opposite of super?

class Parent(object):

    def __init__(self):
        print <ChildClass>.x

class someChild(Parent):
    x = 10

It is a stupid example, but it shows my intention. By the way, using someChild will not work, because there are many child classes.

The only solution I can think of is to have a constructor in every child class that calls the constructor of Parent with a reference to itself (or even to pass x), but I would like to avoid having a constructor at all in each child.

Answer 1

What is wrong with just using self.x ?

class Parent(object):
    x = None  # default value
    def __init__(self):
        print self.x

class someChild(Parent):
    x = 10
    def __init__(self):
        Parent.__init__(self)

class otherChild(Parent):
    x = 20
    def __init__(self):
        Parent.__init__(self)

a = someChild()
# output: 10
b = otherChild()
# output: 20

Note how this works even if Parent has a class attribute x as well ( None in the above example)- the child's takes precedence.

Answer 2

self.x will work if the instance doesn't have an x attribute.

type(self).x if the instance has an x attribute and you want the class's value, essentially skipping over the instance.