code: def step(self, a):
      posbefore = self.sim.data.qpos[0]
      self.do_simulation(a, self.frame_skip)
      posafter, height, ang = self.sim.data.qpos[0:3]
  
      alive_bonus = 1.0
      reward = (posafter - posbefore) / self.dt
      reward += alive_bonus
      reward -= 1e-3 * np.square(a).sum()
      s = self.state_vector()
      terminated = not (
          np.isfinite(s).all()
          and (np.abs(s[2:]) < 100).all()
          and (height > 0.7)
          and (abs(ang) < 0.2)
      )
      ob = self._get_obs()
  
      if self.render_mode == "human":
          self.render()
      return ob, reward, terminated, False, {}
  
file_path: gym/gym/envs/mujoco/hopper.py
imports: import numpy
  from gym import utils
  from gym.envs.mujoco import MuJocoPyEnv
  from gym.spaces import Box
label_desc: Use image node_id 2 for calling the HopperEnv obj's underlying member method code with example usage: obj.step(a) and returns: ob,  reward,  terminated,  False,  dict