<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def step(self, exploration):
 """ Execute one step in any of the runners. """

        if len(self._runners) > 1:
            self._populate_job_queue.put(exploration)
        else:
            self._runners[0].step(exploration)