@abc.abstractmethod<EOL><INDENT>def get_objective_banks(self):<DEDENT>
return<EOL>
Gets all ``ObjectiveBanks``.

        In plenary mode, the returned list contains all known objective
        banks or an error results. Otherwise, the returned list may
        contain only those objective banks that are accessible through
        this session.

        :return: a ``ObjectiveBankList``
        :rtype: ``osid.learning.ObjectiveBankList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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