def step_back(self):
        ''' Take one step backward.

        Returns:
            (tuple): Tuple containing:

                (dict): The previous state
                (int): The ID of the previous player

        Note: Error will be raised if step back from the root node.
        '''
        if not self.allow_step_back:
            raise Exception('Step back is off. To use step_back, please set allow_step_back=True in rlcard.make')

        if not self.game.step_back():
            return False

        player_id = self.get_player_id()
        state = self.get_state(player_id)

        return state, player_id
 Take one step backward.

        Returns:
            (tuple): Tuple containing:

                (dict): The previous state
                (int): The ID of the previous player

        Note: Error will be raised if step back from the root node.
        
rlcard/envs/env.py