http://docs.python.org/lib/built-in-funcs.html

The property function paragraph (version 2.5) includes
the following snippet 

class C(object):
    def __init__(self): self.__x = None
    def getx(self): return self._x
    def setx(self, value): self._x = value
    def delx(self): del self._x
    x = property(getx, setx, delx, "I'm the 'x' property.")

On line 2, __x is initialized. Some think this should
be _x.