Get Callable for specified string (for GUI-based editing)

def eval_in_system_namespace(self, exec_str):
        """
            Get Callable for specified string (for GUI-based editing)
        """
        ns = self.cmd_namespace
        try:
            return eval(exec_str, ns)
        except Exception as e:
            self.logger.warning('Could not execute %s, gave error %s', exec_str, e)
            return None