def get_composition_search_session(self, proxy):
        """Gets a composition search session.

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

        """
        if not self.supports_composition_search():
            raise Unimplemented()
        try:
            from . import sessions
        except ImportError:
            raise  # OperationFailed()
        proxy = self._convert_proxy(proxy)
        try:
            session = sessions.CompositionSearchSession(proxy, runtime=self._runtime)
        except AttributeError:
            raise  # OperationFailed()
        return session