<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def start_download_thread(self):
		'''start the downloader'''
		if self._download_thread:
			return
		t = threading.Thread(target=self.downloader)
		t.daemon = True
		self._download_thread = t
		t.start()