下面，base_id而且_id是一个类变量和所有子类之间共享。
有没有一种方法可以将它们分成每个类？

from itertools import count

class Parent(object):
    base_id = 0
    _id = count(0)

    def __init__(self):
        self.id = self.base_id + self._id.next()


class Child1(Parent):
    base_id = 100
    def __init__(self):
        Parent.__init__(self)
        print 'Child1:', self.id

class Child2(Parent):
    base_id = 200
    def __init__(self):
        Parent.__init__(self)
        print 'Child2:', self.id

c1 = Child1()                   # 100
c2 = Child2()                   # 201 <- want this to be 200
c1 = Child1()                   # 102 <- want this to be 101
c2 = Child2()                   # 203 <- want this to be 201