def __getitem__(self, id_):
return self._items[id_]<EOL>
Get the object with the :paramref:`id`

        .. code:: python

            ic = IdCollection()
            ic.append(object_1)
            ic.append(object_2)
            assert ic[object_1.id] == object_1
            assert ic[object_2.id] == object_1

        :param id_: the id of an object
        :return: the object with the :paramref:`id`
        :raises KeyError: if no object with :paramref:`id` was found