code: def step(self, a):
      ctrl_cost_coeff = 0.0001
      xposbefore = self.sim.data.qpos[0]
      self.do_simulation(a, self.frame_skip)
      xposafter = self.sim.data.qpos[0]
  
      reward_fwd = (xposafter - xposbefore) / self.dt
      reward_ctrl = -ctrl_cost_coeff * np.square(a).sum()
      reward = reward_fwd + reward_ctrl
      ob = self._get_obs()
  
      if self.render_mode == "human":
          self.render()
  
      return (
          ob,
          reward,
          False,
          False,
          dict(reward_fwd=reward_fwd, reward_ctrl=reward_ctrl),
      )
  
file_path: gym/gym/envs/mujoco/swimmer.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 SwimmerEnv obj's underlying member method code with example usage: obj.step(a) and returns: ob,  reward,  False,  False,  dict