Retrieve the single (expected) instance of this 'Part' (of `Category.MODEL`) as a 'Part'.

        See :func:`Part.instances()` method for documentation.

        :return: :class:`Part` with category `INSTANCE`
        :raises NotFoundError: if the instance does not exist
        :raises MultipleFoundError: if there are more than a single instance returned

def instance(self):
        """
        Retrieve the single (expected) instance of this 'Part' (of `Category.MODEL`) as a 'Part'.

        See :func:`Part.instances()` method for documentation.

        :return: :class:`Part` with category `INSTANCE`
        :raises NotFoundError: if the instance does not exist
        :raises MultipleFoundError: if there are more than a single instance returned
        """
        instances_list = list(self.instances())
        if len(instances_list) == 1:
            return instances_list[0]
        elif len(instances_list) > 1:
            raise MultipleFoundError("Part {} has more than a single instance. "
                                     "Use the `Part.instances()` method".format(self.name))
        else:
            raise NotFoundError("Part {} has no instance".format(self.name))