https://github.com/ethereum/wiki/wiki/JSON-RPC#db_getstring

        DEPRECATED

def db_getString(self, db_name, key):
        """https://github.com/ethereum/wiki/wiki/JSON-RPC#db_getstring

        DEPRECATED
        """
        warnings.warn('deprecated', DeprecationWarning)
        return (yield from self.rpc_call('db_getString', [db_name, key]))