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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def manage(cls, entity, unit_of_work):
 """ Manages the given entity under the given Unit Of Work. If `entity` is already managed by the given Unit Of Work, nothing is done. :raises ValueError: If the given entity is already under management by a different Unit Of Work. """

        if hasattr(entity, '__everest__'):
            if not unit_of_work is entity.__everest__.unit_of_work:
                raise ValueError('Trying to register an entity that has been '
                                 'registered with another session!')
        else:
            entity.__everest__ = cls(entity, unit_of_work)