def get_activities_by_assets(self, asset_ids=None):
raise Unimplemented()<EOL>
Gets the activities for the given asset.
        In plenary mode, the returned list contains all of the
        activities mapped to the asset Id 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.
        arg:    assetIds (osid.id.IdList): Ids of Assets
        return: (osid.learning.ActivityList) - list of activities
        raise:  NotFound - an assetId not found
        raise:  NullArgument - assetIdList is null
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        compliance: mandatory - This method is must be implemented.