def METHOD_NAME(self):
    """
    Identifier of this unit, with the provider namespace.
    .. note::
        In rare (unit tests only?) edge case a Unit can be separated
        from the parent provider. In that case the value of ``id`` is
        always equal to ``partial_id``.
    """
    if self.provider and self.partial_id:
        return "{}::{}".format(self.provider.namespace, self.partial_id)
    else:
        return self.partial_id