code: def step(self, action):
      xposbefore = self.sim.data.qpos[0]
      self.do_simulation(action, self.frame_skip)
      xposafter = self.sim.data.qpos[0]
  
      ob = self._get_obs()
      reward_ctrl = -0.1 * np.square(action).sum()
      reward_run = (xposafter - xposbefore) / self.dt
      reward = reward_ctrl + reward_run
      terminated = False
  
      if self.render_mode == "human":
          self.render()
      return (
          ob,
          reward,
          terminated,
          False,
          dict(reward_run=reward_run, reward_ctrl=reward_ctrl),
      )
  
file_path: gym/gym/envs/mujoco/half_cheetah.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 HalfCheetahEnv obj's underlying member method code with example usage: obj.step(action) and returns: ob,  reward,  terminated,  False,  dict