def dof(self):
        """Returns the DoF of the robot (with grippers)."""
        dof = self.mujoco_robot.dof
        if self.has_gripper_left:
            dof += self.gripper_left.dof
        if self.has_gripper_right:
            dof += self.gripper_right.dof
        return dof
Returns the DoF of the robot (with grippers).