subclass_private_methods.py

>>> class A(object):
...     bar = None
...     def __fu(self, bar):
...         self.bar = bar
...     def public_fu(self, bar):
...         self.__fu(bar)
... 
>>> a = A()
>>> print (a, a.bar)
(<__main__.A object at 0x7fd5d0274810>, None)
>>> a.public_fu(10)
>>> print (a, a.bar)
(<__main__.A object at 0x7fd5d0274810>, 10)
>>> 
>>> 
>>> class B(A):
...     rebar = None
...     baz = None
...     def _A__fu(self, bar):
...         super(B, self)._A__fu(bar)
...         self.rebar = 'Python hates me'
...     def __fu(self, bar):
...         raise ValueError((bar, 'sad'))
...     def public_fu(self, bar, baz):
...         super(B, self).public_fu(bar)
...         self.baz = baz
... 
>>> 
>>> b = B()
>>> print (b, b.bar, b.baz, b.rebar)
(<__main__.B object at 0x7fd5d0274950>, None, None, None)
>>> b.public_fu(100, 111)
>>> print (b, b.bar, b.baz, b.rebar)
(<__main__.B object at 0x7fd5d0274950>, 100, 111, 'Python hates me')