gistfile1.txt

>>> class A(object):
...     def __init__(self):
...             self.__foo = 'bar'
...     @property
...     def foo(self):
...             return self.__foo
...
>>> a = A()
>>> a.foo
'bar'
>>> a.foo = 'baz'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute
>>> a._A__foo = 'baz'
>>> a.foo
'baz'
>>> a.__foo
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'A' object has no attribute '__foo'
>>> a._A__foo
'baz'