def get_repository_hierarchy_session(self, proxy):
if not self.supports_repository_hierarchy():<EOL><INDENT>raise Unimplemented()<EOL><DEDENT>try:<EOL><INDENT>from . import sessions<EOL><DEDENT>except ImportError:<EOL><INDENT>raise  <EOL><DEDENT>proxy = self._convert_proxy(proxy)<EOL>try:<EOL><INDENT>session = sessions.RepositoryHierarchySession(proxy, runtime=self._runtime)<EOL><DEDENT>except AttributeError:<EOL><INDENT>raise  <EOL><DEDENT>return session<EOL>
Gets the repository hierarchy traversal session.

        arg     proxy (osid.proxy.Proxy): a proxy
        return: (osid.repository.RepositoryHierarchySession) - a
                RepositoryHierarchySession
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_repository_hierarchy() is false
        compliance: optional - This method must be implemented if
                    supports_repository_hierarchy() is true.