@abc.abstractmethod<EOL><INDENT>def get_activities_by_ids(self, activity_ids):<DEDENT>
return<EOL>
Gets an ``ActivityList`` corresponding to the given ``IdList``.

        In plenary mode, the returned list contains all of the
        activities specified in the ``Id`` list, in the order of the
        list, including duplicates, or an error results if an ``Id`` in
        the supplied list is not found or inaccessible. Otherwise,
        inaccessible ``Activities`` may be omitted from the list and may
        present the elements in any order including returning a unique
        set.

        :param activity_ids: the list of ``Ids`` to retrieve
        :type activity_ids: ``osid.id.IdList``
        :return: the returned ``Activity`` list
        :rtype: ``osid.learning.ActivityList``
        :raise: ``NotFound`` -- an ``Id was`` not found
        :raise: ``NullArgument`` -- ``activity_ids`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*