Au contraire, double underscore does make it "private". Trying to access a double underscore attribute directly will throw an AttributeError.

    >>> class Foo(object):
    ...     def __init__(self):
    ...             self.__a = 42
    ...     def look_here(self):
    ...             print self.__a
    ...
    >>> f = Foo()
    >>> f.__a
    Traceback (most recent call last):
      File "<stdin>", line 1, in ?
    AttributeError: 'Foo' object has no attribute '__a'
    >>> f.look_here()
    42