code: def _frame_limit(self, start_time):
          
          if self._speed:
              completion_time = time()
              exc_time = completion_time - start_time
              sleep_for = (1.0 / abs(self._speed)) - exc_time
              if sleep_for > 0:
                  sleep(sleep_for)
docs: Limit to framerate, should be called after
          rendering has completed
  
          :param start_time: When execution started