@abc.abstractmethod<EOL><INDENT>def get_agents_by_agency(self, agency_id):<DEDENT>
return<EOL>
Gets the list of ``Agents`` associated with an ``Agency``.

        :param agency_id: ``Id`` of the ``Agency``
        :type agency_id: ``osid.id.Id``
        :return: list of related agents
        :rtype: ``osid.authentication.AgentList``
        :raise: ``NotFound`` -- ``agency_id`` is not found
        :raise: ``NullArgument`` -- ``agency_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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