Python inheritance class variables

Question

I've a base class.

class Base(object):
    CLASS_CODE = None  # This value should be set in sub-classes.

    var1 = 'E%s001' % (CLASS_CODE)
    var2 = 'E%s002' % (CLASS_CODE)


class Child(Base):
    CLASS_CODE = 'Child'

Now, I want to call, Child.var1, it should be EChild001, it rather gives ENone001.

How do I achieve the desired functionality?