code: def start(self, interval, now=True):
          
          if interval < 0:
              raise ValueError('interval must be >= 0')
  
          if self._running:
              self.stop()
  
          self._running = True
          self._interval = interval
          if now:
              self._self_thread = hub.spawn_after(0, self)
          else:
              self._self_thread = hub.spawn_after(self._interval, self)
docs: Start running pre-set function every interval seconds.