class Klass(object):
    my_list = [1, 2, 3]


class KlassMeta(type):

    def __new__(cls, name, bases, attrs):
        attrs['my_list'] = bases[-1].my_list + [4, 5]
return super(KlassMeta, cls).__new__(cls, name, bases, attrs)


class SubKlass(Klass, metaclass=KlassMeta):
    pass
Accessing parent class attribute from sub-class body