private.py

def private():
    """
    Factory function for creating Private instances.
    """
    
    def _():
        _.attr = 0

        class Private(object):
            """
            class with one private attribute and method to increment.
            """

            @property
            def attr(self):
                return _.attr

            def add_one(self):
                _.attr += 1

        return Private()

    return _()