请教各位python类的私有方法不能在子类方法中覆盖吗

#!/usr/bin/env python

class Base:
    def __a(self):
        print "private method __a in Base Class"
    def a(self):
        print "public method a in Base Class"
    def b(self):
        self.a()
        self.__a()
class Derived(Base):
    def __a(self):
        print "overwrite private method __a Derived Class"
    def a(self):
        print "overwrite public method a in Derived"

d = Derived()
d.b()

Base类里的self.__a()实际是self._Base__a()
而且__开头的本来就是表示private,private是不可继承的

多谢！