def step_wait(self):
raise NotImplementedError()<EOL>
Wait for the step taken with step_async().
Returns (obs, rews, dones, infos):
 - obs: an array of observations, or a tuple of
        arrays of observations.
 - rews: an array of rewards
 - dones: an array of "episode done" booleans
 - infos: a sequence of info objects